First of all , welcome to TSF.
A home theater PC can be a good addition to a HT - but only for digital files for which it has access. I don't know of any that can act as your receiver does and switch between source media. You best bet is to build your HTPC and make sure the sound card can accept stereo in. (I've never seen one that cannot). Then convert all your old media to digial file using software on the PC.
HERE's a linux based guide for example.
Once its in the PC you'll be able to use the media library software to play any piece.
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If there are lawyers or politicians involved, logic may be a very poor tool for reaching a conclusion.