An ADAT type interface would allow to take all eight tracks to be edited and mixed on the computer. But the tracks would get there "as is", that is, no mixing before the computer. If this what you desire, then yeah, there are card that do it. I would think your best bet is to go to the Alesis forum and get Ed to answer you question. He seems to work extensively with ADATs and computers and he will probably get you to the sound card you need.
Now, if you are looking to get your mix on the computer and bun a CD with your mix, you can just go out from your mixer to the line in of your soundcard, record your music on the hard drive and let your CD software do the rest.
Peace, Jim
