So this works?
Directsound
WASAPI
But this doesn't?
ASIO
That seems like a driver problem. Does it work from MC, not using WDM? You should get the same behavior. WDM shouldn't matter.
32 bit MC would be worth trying.
Okay, just to be sure I made a clean install of Windows (same version) and installed both JRiver x86 and x64. Both seem to fail in the same way, but oddly enough, now the ASIO driver seems to only be able to play through the onboard speakers when opening a FLAC file.
If I try to play either the WDM stream or the FLAC file through both DirectSound and WASAPI everything goes smoothly on both architectures, so given that not even the onboard speakers seem to be able to play through WDM, I'm kind of stumped on what else I could try to diagnose the issue.
So far, the only thing that seems consistent is that when trying to open the ASIO stream with the IPC stream, JRiver stutters heavily until I manage to change it back to any other output device, but aside from that nothing can continue working within JRiver itself while the connection is attempted.