If you’d really like the best sound possible in 2-channel, your best bet is to completely remove your AVR from the signal chain when listening in stereo. Neither the Pioneer’s amp section nor, just as importantly, its preamp section are doing you any favors in 2-channel sound quality. The easiest way to do this is to buy a dedicated integrated stereo amplifier. This way you can completely remove the AVR for more critical stereo listening literally with the push of one button if the integrated amp has a HT pass through feature, but you can continue to use your AVR for multichannel preocessing and to power your center and surround speakers. Believe it or not, you simply hook the AVR’s front L/R preamp outs to the HT pass through input on the integrated and hook the speaker outs from the integrated to your front L/R speakers, and you’re done. It’s literally that easy.
Not sure what you were prepared to spend on a new amp, but for around $1500 you could get a Hegel H160 or an Ayre AX7e available here now, both of which offer HT bypass and will significantly outperform your AVR for stereo listening. Bypassing your AVR completely in favor of either of these integrateds will likely far outweigh any benefits of just replacing the amp to bi-amp. You can probably buy some used shotgun biwire speaker cables down the road with this setup and get a good portion of biamping anyway. Just my $0.02, and best of luck.
