While working on my QAM Mapper for the HDHomeRun, I was running GB-PVR, MediaPortal, BeyondTV trial, MCE and various other PVRs at one point. All installed together but only starting one at a time. So yes it's possible for them to co-exist. I suggest making a backup of your system if possible before you load them though. When you are done testing, reload the backup and install the one you decided on.