If you want a good interface, you should choose Motu. I've been using a Motu 2408 and maybe it would be a good choice for you.

With this interface you have 3 banks of 8 channels wich you can individually set to Analog (only on the first bank), TDIF or ADAT.

Then you would only need a digital mixer with ADAT or TDIF in order to get 24 in/out to your computer!

Luis Santos