My question is, what mics do you have? But here is my answer to your question.

When I leave the house with a truckload of gear, if I have one box that does everything and sounds good, I always take that instead of two boxes that need cables and power supplies, setup and teardown.

Fact is, the quality of the sound is mainly mics and mic placement.

I have both digital mixers (and analog, and all-in-one recorder/mixer combos), and in situations where I need the mixer, I always use the DR 680. It is true that the mixer can be adjusted a bit quicker, but if you are recording on separate tracks, it is only an isse for feeding on site devices. And, once you get used to it, the DR 680 is easy to use.

And the 680 is eight fracking channels in one box, with a real headphone jack, a digital mixer, and analog outs.

You can also combine the 680 with an RME device to create a super accurate clock and digital patchbay using totalmix. However, you likely will not need this. Totalmix is the best routing system I have used for digital distribution. But I just take the tracks home and mix them in post. Why not?

You might need a mixer if you have a very complex sound distribution system, and here I'm talking a powered mixer and/or powered speakers, for a big rock show, a play, musical theatre, etc. But in these cases, you will be more than likely to be feeding a FOH system that is in place.

Noise: not an issue with the DR 680 or, in fact, almost any other system made today. If you have a really noisy microphone, replace it. Recently, people have been doing blind AB tests with midpriced gear, like the Mackie Onyx and Focusrite, etc. And no one can tell the difference compared to stuff costing many thousands of dollars. However, in a live video situation, the ambient noise will never go below 20 dB and in fact can easily be in the 30s, so 1-3 dB noise figure is completely irrelevant. That means if you buy an RME Octamic, which has a noise figure of 129.5 EIN, which is the absolute theoretical limit, or the Benchmark pre which has a 1dB noise figure, and you compare it to the Mackie which is around 127-129, depending on the model and the power supply, you will not hear a difference. I've tested it, retested it, and tested it again. The DR 680 is really quiet, But suppose it wasn't, suppose it was 2dB nosier, no biggie--it is way below ambient.

Gain: if you need gobs of gain, the RME digital preamps have gobs of gain, and there are a few others as well. Usefull for ribbon mics. The DR 680 has enough gain for my ribbons, not like the RME UFX, but still plenty, and it doesn't fuzz out when you push it like a lot of the cheesy pots on cheap mixers.

I think PB's point is a good one, which is you need to think about exactly what is going to happen during the shoot. Who is going to run what, and how it will work. Multitracking frees up someone to run a camera, you don't need to ride the gain. In fact, once I set up the 680, I just leave it and go work a camera. (I use my FR2LE to record the stereo mix as a backup, or split the main pair as a side feed in case the 680 goes down.)

Boxes come and go. They last a few years. Then something better comes along. I have some really great, hand made mic pres that are no ten years old, and they still sound amazing. In the old days, you would spend $3,000 on a stereo pre, $2000 on a converter, and $1000 on a DAT, and voila, you were (and still are) truly audiophile.

But when I leave the house, I throw the DR 680 in the bag. I consider this progress. And don't forget the microphones.

I have a Sound Devices MixPre, one of the best investments I ever made, but I have to say its nearly impossible to be a good camera man and sound man at the same time. If I need good sound I attach a Rode NTG-2 to the top of my GH2 and run it directly into the camera. Using any separate recording devices like the zoom can be tricky as you increase the chances for mistakes like forgetting to press record on one or the other device, or any number of issues that need to be dealt with.

But if you think you can figure out how then just try it yourself. Borrow some gear and see how it all works.

@DrDave then what would you recommend if someone had a soundman (well, just a boom operator), but was on a tight budget? The setup is for a movie - just boomed microphones, no lavs. Does it still make sense to get a mixer and a preamp in addition to a field recorder? if yes, which one? Or would it suffice to have the shotgun mic going directly into something like Roland R-26,which has its own 2 level controls and its own built-in preamp? The goal is to achieve a very deep and "involving" film-like sound.

@spacewig thanks. That's the whole issue - the setup is really simply, just 1 boom mic at a time. So no need to mix anything. But I was under the impression that Mixers also have preamps. So far I've been recording using a really cheap Chinese shotgun microphone EM320E direct to Zoom H1. The results are quite nice - the hiss from EM320E is minimal and when minimized in post, it's quite warm and pleasant actually (reminds me of Hollywood classics from 1970s, Godfather, Taxi Driver etc). But cleaning up each audio clip like that is a pain in the neck, plus it's not a great mic for internal dialogues (room tone, reverb etc) so I'm thinking of getting Oktava MK-012 + Rode NTG2 (or Sennheiser MKH 416) + Roland R-26, which (they say) has it's own preamp and 2 mixer-like level controls. So the question is, do I still need a mixer with a preamp, or just a preamp like SoundDevices MixPre, or do I need to just get Roland R-26 and that's it?

I think there are a couple of issues to consider. One is whether you are going to mix down everything on site, or record it all in separate tracks to fine tune later. Most of us who want the best sound will mix it down in post, just like we will grade the color in post. But there is a trade-off--time is money, etc. So if you don't want to bother, then it is important that your field mixer have easy to use knobs with a large, easy to read screen. You Don't want to be churning through menus on location.

Now with a a DR 680, you can multi-track all the tracks and mixdown to stereo, so you can then decide later whether to bother remixing the sound. But because it is relatively small and compact, it isn't designed to ride the gain (turn the knobs up and down on the fly). But nobody really rides the gain anymore, because if you record in 24 bit, you don't need to--it is like having the ability to crop in full frame.

So basically, you can't go wrong with the 680, and if you get the field mixer, you can go wrong, but it can be a timesaver in skilled hands. Great sound, mixer built in, multi-track built in, great pres, limiter, everything you need. No big knobs, but easy enough to use once you figure it out.

Digital mixer settings: let's say you are doing a shoot spread over several days. With a field mixer, the settings are often analog. That means you won't get exactly the same settings day to day, unless you leave it on site and don't even breathe on the settings. With a RME box (love RME) or the Tascam DR 680, and many others of the newer style, the settings are the same because they are digitally stored, so day one sounds like day two, which can be a real issue if it isn't right.

The multitrack gives you bigtime CYA. You can have a backup mic or mix on a separate track, a stereo submix for an external feed, etc, etc. And for me, I don't want the stress of going, Ruh Roh, my audio is messed up and I can't fix it 'cause I mixed it down live and that is all I have.

What s@pacewig say is right--if you are just using one or two mics and you never will use more, get something simple, like the Tascam he mentions, or just a Zoom H2N. The zoom has everything you need in a small, compact box that works as a mic, a multitracker, an ms setup and even a quick and dirty surround sound recorder. Cheap, great mics, etc., etc. MS is a very, very powerful tool for recording on location as you can adjust the pickup pattern in post. Put the mics in the wrong place? MS can help. MS is a zillion times easier to use than in the olden days.

The new boxes are dream boxes. Imagine lugging around the monster machines of yore, that cost more and didn't work very well.