That's unfortunate. In my situation, I have three PCs... my main one (email/browsing), a work PC, and my gaming PC. I have to share my keyboard, mouse, monitor and speakers with all three, as they are all side by side and there's no space for multiple workstations.
I've been using Multiplicity for many years, but it seems that recently I've been experiencing the issues listed, after getting a new game PC (secondary). Most of the games work fine, but some that are first person (rotate view with mouse moves) have some type of issue (different between games), and that odd thing where the KVM shows a black screen during a load (not a game-breaker, but I was curious why that might happen).
One option would be to take the gaming PC off the KVM, add a 2nd (local) keyboard and mouse, and pipe the video through the flatscreen TV that is beside the computer monitor. I discovered that the audio is actually sent through that connecting cable to the flatscreen, so I could even get audio... but it's a shame my gaming has to use that inferior monitor speaker, rather than the dedicated speakers I currently have shared with all three. It's too bad I can't specify what MP KVM controls (ex. mouse, keyboard, etc). All I see that can be turned on/off is the audio, but I kind of would need the opposite... where I turn off everything except the audio, so the audio would go through the Ethernet KVM cable and be sent to the dedicated speakers.