For lack of a response from someone who has actually tried getting ASIO working on such a setup, I suggest you just try it. Grab a Live CD and a spare external

For lack of a response from someone who has actually tried getting ASIO working on such a setup, I suggest you just try it. Grab a Live CD and a spare external hard drive and just give it a whack. Passing through the sound cards should work. USB might be trickier if you're not just passing through a whole USB hub. But considering how new IOMMU is, I imagine the intersection between people who have tried it and people who use Cubase is incredibly tiny.