Using an audio dock on CM10.1 i9100
I know that this has been fixed in some of the latest CM10 nightly releases. As a matter of fact, I'm running JellyBam 4.1 (based on CM10) and the USB audio does work without issues. When I've updated to JellyBam 5.2 (based on CM10.1), USB audio stopped working. So I had to revert back to 4.1, which is, in my opinion, an excellent release anyway.

I've read in forums that the problem is not proprietary drivers or anything like that (it is working on CM10 nightlys afterall), but rather than CM team has not finished implementing all audio features on 10.1 yet. The need to migrate this patch to CM10.1, that's all.

So my advice is to install CM10 nightly or JellyBam 4.1. You will enjoy Android 4.1.2, and of course, your USB audio.