So... I think I've found a weird conflict between Parsec and my Vive. I've already made a thread on the Steam forums about it, link here:

The short version is I get a 15000 error in Parsec if I attempt to connect to my PC (the host) while SteamVR is running. If I exit SteamVR, connect with Parsec then attempt to run SteamVR again (with or without being connected, even without Parsec actually running on the host), I get error 208 in SteamVR, the only fix is to connect with HDMI instead of DisplayPort, reboot, run SteamVR, exit and reconnect with DisplayPort. Really odd, I'll keep plugging away at it (hopefully not by literally plugging and unplugging the DP and HDMI cables) and see what I find. Thought I'd report it here just in case anyone knows what's happening or is interested for any other reason. Thanks!