What is the best sounding Pre/Pro 7.1 channel with analog bypass.

When talking about Y-adapters, you must be very careful.  You can use a Y Adapter to connect your Oppo or source to multiple amps.  However, you must never use a Y adapter to connect multiple sources to the same amp.  The signal will feedback into the second source and fry the output stages of that source.
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That being said, I would say either Krell S1200 variation or a Bryston SP3.  Both have slightly different sounds.  Both have fully discrete Class A audio stages for both input and output  Bryston has excellent bass, but it somewhat laid back in the mids and upper mids.  The Krell will not have as strong/deep bass, but it has excellent resolution and attack - much more exciting in my opinion.  The Krell can sometimes sound a bit bright/thin in some systems.

Parasound P7.

No need for Y adapters. Its' a very good 2 channel preamp that has an extra 5.1. :)

It is much better constructed and sounding than the P5.

Hey Erik, he needs HDMI input/outputs.  Otherwise, I may have included P7.  But then again, he's asking for the "absolute best pass-through HT Processor".

What is your priority between stereo and HT?  What's your budget?  What sound characteristics are most important to you?  What speakers are you using?  Right now, IMO you're just organizing deck chairs on the Titanic.  Take a step back and let us know the answers to the important questions above and you'll get much better and more effective recommendations here. 

I looking to spend about $500 or less for a used pre/pro. So from $700 to $1000 new. Seeking clarity and imaging in the sound quality. Used mainly for HT, but want great sound for stereo. Using Chane bookshelf speakers with an Elac powered subwoofer in a 12'X12' room.