So, update; this appears to have fixed my sound issue, but unfortunately, LatencyMon reported bighuge numbers again. I'd been going through a list of potential offenders to try to push it - but seeing those 18K latencies again was just incredibly disheartening. I don't feel comfortable randomly reseating my drives, I don't feel comfortable doing a 'repair install' that'll undo everything I've spent so long customising, and I surely don't want to do a full reinstall. Is what it is. Maybe this will help someone with similar issues, though.
