I presently have a 2 in/ 2 out sound card from emagic and I am looking around for an upgrade. I need an 8 in 8 out card lwith an external AD/DA converter ike the MOTU mk2/3 or the Aardvarkq10 etc etc. - the reason being, I'd like to record drums with a track per mic. (as you can imagine, trying to record drums on just two tracks is hard work)

However, I'm trying to imagine just what I would need. I have a 16 track, analogue, mixing desk with 4 subgroups. How would I connect to a breakout box? Would you normally go via the subs or take a direct out from each individual tracks? How do people who have bigger desks than mine (i.e. 8 subs or more) do this?

I'd be grateful for any advice concerning just how to connect the desk with the external converters (or would you just go straight into the converters?) and particularly any recommendations for semi-pro quality sound cards (I'll probably buy it second hand so recommendations for cards that are no longer available or older models are also welcome)

PS - I need at least one digital in/out if anyone is thinking of suggesting a specific card

Well, for every drum mic you'll need a preamp. If the A/D converter you choose doesn't have onboard preamps, you'll need to use your mixer's. If you want each mic to have it's own track you'll want to send the direct outs from each channel on your mixer to the corresponding channel on the converter. I can't think of a reason to use subgroups in this case unless you want to combine tracks before sending to the converter (not recommended).
I think you're on the right track with MOTU, Aardvark. You may also want to look at Lynx, maybe used Apogee if you can find it. A/D conversion is critical, don't skimp if you can help it.
Good luck!