For those looking for high bit rate, non-usb, stable multi-channel input and output on the pi (6 in 8 out), this current Kickstarter may be of interest. I'm not affiliated with the guy responsible for this , but I do have his first board, the 2 in 2 out version. So far it seems very stable at reasonably low latency settings in JACK and has the added benefit of mainline kernel support. If the multi-channel version works nearly as well it may be a winner.