Fist it depends on your HTPC use case. You would have to be running an application on the PC that can avail itself of madVR. Right now that is limited to MP-HC and JRiver MC for the most part. Now JRiver attempts to be an all emcompassing MediaCenter solution and it matches MP-HC for video playback. Sadly its PVR and EPG presentation are far inferior to WMC nor does it currently support Cable Tuners. I own JR MC18 but mostly watch it and wait. If the EPG/PVR evolves to WMC levels and it get reasonable support for the Ceton tuner. I can standardize on it. It is really then when madVR and a first quality 3D LUT puts us in a new ballpark. All the pieces come into place to have accurately calibrated displays at the highest level wherever an HTPC is attached. The idea of a single integrated source solution comes to the table.
This largely gets away for the need for external boxes like the Radiance.. One source, to render all content at the highest level while also correcting display deficiencies acheiving reference or near reference quality display output using a single consistent interface.Of course JR will have to stop adding 10k features a week and start focusing on bug killing. Sadly, they are more focused on porting their app to the Mac then building a robust EPG/PVR enviroment. They do have file playback largely perfected thanks to madVR and LAV.