Whats the rest of your system spec?
When I had DPC issues on my system USB+Audio drivers was the main issue... Long story short
After months trying to fix the issue I changed to windows 8 and I was doing step by step till the issue came back, what I found was a surprise. I had an SSD 60GB a caching drive to a 2TB hard-drive it was this that was making the Audio stutter and skip..
What I trying to say here, is just because the issue is pointing towards DirectX dont rule out something completely different giving the issue.
Oh I agree. The same setup was fine with identical hardware and configuration running 2 7950s though, and I have also tried a clean install of windows so it should be a fairly isolated issue. That and the fact Matt confirmed it as a replicated issue makes me fairly certain that it isn't just on my end.