Tell us how big your room is (LXWXH) and describe how loud you listen and what you don't like about your current sound.
But smart money says:
Return the Pioneer receiver and start looking for new speakers!
The Onkyo you have is not a great receiver, but it is not a piece of crap either. With the Polk Monitor 60's rated as 8 Ohms and 90dB sensitivity, the Onkyo 65WPC should be sufficient (unless you are trying to play loud in a large room).
The differences between receivers are nothing compared to the differences between speakers, and if you don't like the sound, changing the receiver will only make a noticeable difference if the receiver was not capable of producing the power needed by the speakers.