After a bit of digging it looks like OSS support is a no-go. The Mk2 has a CS4231A codec. It seems the empeg CS4231A driver is implemented as a simple character device, so it has no OSS support. I guess the driver for the Mk1 had OSS support.

In any case I don't think I can get it to work that way, unless you have another idea. I guess I'll have to focus on PortAudio.