I'm using Sonar 8.5 and I have two audio interfaces - a Layla 3G (PCI) and a Tascam US-1800 (USB). Sonar will recognize one or the other but not both at the same time. Does anyone know why these interfaces will not work simultaneously (perhaps because one is PCI and the other is USB)?

The ASIO specification only allows one I/O device at a time. Could that be the issue?

Well I'm able to run either 2 Laylas (or 2 Delta 1010s) simultaneously but perhaps that's because Sonar uses the same driver for both units. I've never tried this before but if I have time I'll try using a Delta unit with a Layla.

WDM has no restriction. In the case of ASIO, some vendors write their drivers to support multiple interfaces but that is up to the writer of the device driver not the DAW.

Cool, thanks for the info. I was originally asking the question (and trying to use the Tascam) so that I wouldn't need to pull my 2nd Layla from my home rack, but I'm running out of time and need to get set up for this afternoon's recording gig so I went ahead and used the Laylas. After this gig I'll experiment with recording using a Layla and the Tascam with WDM.