So, nice of everyone to come running with advice, s/ but has anyone ever heard of this problem? Is this a known glitch in the newest version of Reaper by any chance?
Okay, so for some reason Wave Out appears to be the only option that's failing. I can get WASAPI & Direct Sound to work. ASIO also works, but I'm using an alternate USB speaker system instead of my interface. So I guess I can get the thing to work under other circumstances.
I remember myself and others had issues with Wave Out before causing REAPER to freeze up. Wonder if that's an issue that needs to be addressed?