First, you will not find a pre/pro that natively decodes DD TrueHD via anything BUT HDMI, so your $500-900 is out of the question without using analog inputs (5.1 or 7.1) and besting the older Proceed gear for audio is tough.
Proceed was made to 'experiment' in the Mark Levinson line without risking the ML name, so many thing made under Proceed were REALLY good for the money (IMHO the HPA 2/3 amps are still exceptional and rival the 400 series ML amps at a fraction of the cost.)
Even if you currently own an AVP, it won't bring much in resale value, so you are still likely under $2K for a pre/pro, which gives you older used (non HDMI) or the likes of the Marantz SR8003 or Integra pre/pro's.
You could get a used Classe SSP600 for about $2K which would do what you want and sound very good, different than the AVP, so you will need to see if its an improvement or not to you sonically but it would allow MC analog inputs, not sure about second zone but believe it does this too.
I don't think the older Anthems nor current Anthems will best the AVP for music, and as you said Maridian won't work for you. Older Krell's are a good choice, one you might look for is the old Audio Video Standard that come up some times for cheap and are really well made and sound quite good.
The PAV/PDSD from Proceed was a great piece but you'll need to modify the connector for MC Analog inputs and they are pretty old and many are reaching failure and they are expensive to fix so I would steer away from these, even though sonically they are better than your AVP.
