Will the VSX-53 convert the 5.1 audio from the PC to stereo for Zone 2?
Yes, but it is not listed as an actual Zone 2 Setup.
If you use Speaker A + B ON, then Speakers "A" will have the 5.1 Audio of the Source, (your HTPC) and the Surround Backs will also have your Source Audio (HTPC)
but be downmixed to 2 Channel (Stereo)
Look on page 53 of the OP Manual top of 3rd column from the Left, SP A + B ON:
SP: A+B ON-Sound is Output from the "A" Speaker terminals (up to 5 channels depending on the source), the two speakers connected to the "B" speaker terminals
and the Subwoofer.
The sound from the "B" speaker terminals will be the SAME as the sound from the "A" speaker terminals (Multichannel Sources will be downmixed to 2 channels)
So when you want your HTPC to be in both places use Speaker A + B ON!
Also the VSX 53 with it's 2 HDMI Outs, you could use the second HDMI Out to run either a HDMI Cable or if it is a really long run, use CAT5e or CAT6 cable the Zone 2 HDTV, provided that there is one.
Then you can See and Hear the Audio through the HDTV or the Speaker A + B Setup, or a seperate power amp as I suggest below.....
Correct me if I am wrong.
Couldn't you also use the Pre-Outs to a separate Power Amp or Cheap receiver (with an HDMI Input) for your Zones.
The cost of a SC55 is $600.00 more than the E53, a Power amp / receiver could probably be found $100.00 to $200.00 or less?
There are also 4 channel amps and you could have Front L & R, Center and a Mono Surround.
You then could either place the amp next to the VSX 53 and then run speaker cables to the Zone OR run the audio connects to the amp at the zone for volume adjustment.
MonoPrice probably has cheap Audio connects depending on the length of the run.
My brother has a nice setup in his backyard, cable with two TV's and a very cheap receiver in his very large Gazebo by the pool.
The reason that he does not put expensive stuff back there, is because they are always outside and exposed to South Florida's harsh Weather!
They do not get wet, but it is very Hot and Humid, not a great area for electronics, but when they finally succumb the the outdoors, he replaces them.
There is always more than one way to skin a cat! LOL!
Just take off the blinders and as Larry the Cable guy would say, "Get 'er Done!" LOL!
You can figure it out and "Get er Done" with the Elite VSX 53!
Just My 2c,