I think your current setup is actually quite well matched. People who reside on the Audiogon forum will pretty much universally dislike both Japanese receivers and Polk Audio loudspeakers, but if you enjoy what you're hearing, then keep enjoying them.
If you really want to move up, then begin by listening to as many other loudspeakers as you can. Visiting the local audio showrooms is OK, but your best bet is to meet other local audiophiles and listen to what they have. Learn why they made the choices they did, both in loudspeakers and amplification.
I have plenty of opinions myself, but what you really need to do is get more experience with the gear others own.