The only chips I'm aware of that support the asynchronous mode in hardware are the 1020 and the 3200, both of whih require firmware changes to do so. I do not know of anyone that has successfully done this programming. I've been working on it for almost a year now and have yet to succeed. I'm going to be working on it this year and might get it working.
Creative used asynchronous mode in the 2NX, but they did not use an audio specific USB chip. They wanted to use USB2.0 so they picked a generic USB 2.0 interface chip and wrote their own firmware for that, implementing aynchronous transfer while they were at it. Even though they used asynchronous they still did not achieve really low jitter performance, it was not a criteria for the board. Thats what I mean by saying that if you use asynchronous you STILL have to do everything else right to get really low jitter.
The results from direct I2S adaptive mode are very good, much better than I expected, but of course there is still room for improvement by going to asynchronous.
John S.
