Personally, I don't have an audio interface of acceptible quality that works with my main machine since I got a laptop without a Firewire port (well, ExpressCard) and I'm on Linux, so the selection of working interfaces is limited. I have legacy setups running, but I'd like to get rid of them.
I've actually been meaning (for months) to beat the STM32F4Discovery code into shape (it's a very quick hack) and make a small expansion board as a shield for the small F407 board my mate did a while ago to have a DIY audio interface -- but obviously, I'd just end up with something like half an Axoloti. So my first thought was just to use this hardware that I have now which has very nice stereo I/O.
Then, of course, I got the idea that instead of just reusing the hardware, I could make it work with the Axoloti software -- just have an object for USB audio I/O like the audio objects, so you could filter things on the way in or out. I'd forgotten about the USB1 limit to begin with, of course, so I was imagining more streams between the computer and the Axoloti, but it'd still be somewhat interesting as a proof of concept, I think. I think of the present hardware as a first generation, anyway, and assume that faster connectivity and more audio I/O is somewhere on or over the horizon.
In short, the synchronization is less of an issue for me to begin with (since I don't need to worry about a second interface), but I'm honestly not familiar with the details of the USB audio class.
I'm reading the source and we'll see what, if anything, happens. I could use one of my two 'loti as a dedicated audio interface (replace firmware completely), but it seems like a waste.