@blindjim - I see that you are really pushing the idea of a AVR Receiver. I don’t think this is really in autre’s best interests as he already has a Red Dragon S500 amp. If he is wanting to improve the sound, I would suggest a dedicated HT Processor instead of an AVR. Sure, the AVR is a great band-for-the-buck one-size-fits-all solution, but it is a compromise when compared to separates and also the OP here is not in that situation. The money spend on a receiver could be better spent towards an HT Processor that would yield better results for his amplifiers (better audio stages, better power supply, XLR outputs, etc.).
I am trying to respond to the OPs exact questions instead of going into an entirely different direction. I do agree that the Oppo players are a good solution, but if you look way back to my first post, I recommend an Oppo player PLUS a Parasound P7 preamp (multi-channel preamp). The Oppo by itself can be used to drive an amp directly, but the sound will be somewhat on the dry side and the Oppo does not exactly have the output gain that a preamp will have.
So, for autre’s recommendation, I would either say a nice HT Processor or an Oppo + Parasound P7. In either case, he has the ability to grow with adding a center channel speaker/amp if he wants to.
@autre - with regards to Oppo 105 vs 203. I would say that the 105 would have better sound because of linear power supply and fully balanced left/right outputs. That being said, if you get the 203 and upgrade it with a linear power supply (i.e. OPPOMOD), it may be VERY close to the 105 sound quality and has the ability to support 4K modes. However, keep in mind that the 203 does not support streaming services directly (such as Spotify, Pandora, Netflix, etc.)