I have a small studio where I record bands and they always comment on the fact I don't have a desk.
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I just can't seem to get my head round how I would benefit from having a desk there??
Well, first of all, it would shut the bands up

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Actually, that's only half-joking. Half the gear most studios choose and have is to have an impressive-looking gear list with which to attract customers.
More seriously, first, good quality analog mixers just have a sound that cannot be replicated digitally. Of course if you're talking a budget mixer, than all bets are off on sound quality.
Second, a decent analog mixer also acts like a manifold for the studio; a central control for distributing and managing the signal path to and rom not only the computer, but to outboard analog gear, which also has characteristics difficult to replicate with digital plugs.
Third, many folks just prefer the feel and workflow of a physical control surface to that of a keyboard and mouse.
Fourth, if you have a digital mixer that also acts as a DAW controller, you can get the best of both a physical analog mixer and a physical control surface for you computer DAW software.
Is there a desk I could route all the channels through and then individually into the interface with good preamps.
For a very nice quality and good-sounding mixer that you can use as a front for your interface, check out the ATB series from Toft Audio.
For a rather nice basic digital mixer that's great for both studio and live recording ans well as basic live FOH, Check out the Presonus Studio Live series. We use one of these in our studio ourselves and have been quite happy with it. An advantage with this is that it also has built-in 16x18 Firewire, connecting directly to your computer. This means you can sell your interfaces if you wish and use that money toward the mixer.
For a combination digital mixer and DAW controller combination, check out
the Tascam DM-3200 or DM-4800. Does basically what Presonus does, but also acts as a complete control surface for your DAW software.
G.