Thats funny, I was just looking at audio cards today too.  M Audio is the way to go.  If you just want audio for it, use the original wing card you spoke of.  You will just need to mod the case a bit.  There are several usb solutions too.  I suggest if you want the usb route, go to http://www.macsales.com.  That is OWCs website.  They have a good selection of Mac stuff.