I use 3 "esynched" EchoAudio Darla 24/96 cards.
That breaks out 6 in's and 24 out's.
I can use my mackie 24x8 (abd route through all my outboard gear) with this set up OR keep everything in Sonar and sound forge and mix digitally.
Ive only been using this setup for a short time. I am so far finding this configuration to be very versatile.
-Alex