here's my setup....
Delta 1010, 2 Delta 410s
That's 12ins/24/outs
The 8 inputs on the 1010 are connceted to the 8 busses on my board, the 8 outputs are connected to tape returns 1-8 on the board
The 8 outputs from the first 410 are connected to tape returns 9-16 on the board
The 8 outputs from the second 410 connect to tape returns 17-24 on the board
(I don't use the 2 inputs on both 410s because they are unbalanced)
SO no matter what channel I plug a mic into on the board I can route it to a buss 1-8, whichever input on the 1010 I want to record through
All tracks (up to 24 of them) in my software can be routed out to an individual output through one of the cards letting me add outboard effects like compressors, reverbs, delays, etc.
From the board I can set up monitor mixes to send to a headphone amp so everyone gets to record in real time with no fear of soundcard latency
Get it?
That's just one way of doing things but if you're just using a cheap ass mixer it's probably better to stay in the box to save all them A/D D/A A/D conversions.