Like you, I went from a Pioneer Elite AVR powered by separate amps and had OK 2-channel sound. When I replaced my Pioneer Elite AVR with a Marantz AV7702 home theater preamp, I was shocked at the difference. The sound was much more life-like with a better overall balance from the highs and lows. One thing I always felt I missed with my Pioneer Elite AVR was mid to low bass with my Magnepan IIIa speakers. Once the Marantz AV7702 was put into the chain, it was like my Magnepans were a completely different speaker. More mid and low bass with clearer mids and highs.
Better 2-channel music
My system consists of the Marantz SR7007, a pair of Emotiva XPA-1 mono blocks, Emotiva XPA-3 for center and surround, Rythmik 15HP sub, Oppo 103, Focal 1000 Be II series front and center, Infinity IL10 surround and back. I listen music from CD and different digital sources and movies from bluray DVD and Netflix, Amazon... My complaint is the Marantz doesn't deliver the quality of 2-channel audio as I expected. My plan is to upgrade either to Emotiva XMC-1 or Marantz AV8802. All suggestions and advices will be greatly appreciated.