Such agendas! You have a listener using an AVR as a preamp asking for the obvious upgrade path and people are suggesting network tweaks, cable upgrades, their favorite DACs.
Come on people! The obvious upgrade is a preamp, as the sane posters have suggested.
Reasoning: the preamp in the AVR is tuned specifically to the amps in it. It may sound OK as a preamp, but it’s intended to be mated with the amps in the AVR. Manufacturers do not invest as much in making the preamp section of an integrated amp work with many different amps, because they are together. The bypass is great as a convenience, but it’s not intended go give the requisite synergy with just any amp. Get a real preamp and see how that sounds!