I like and agree with the advice given so far. I want to add the complication, that depending on the age and initial cost of your AVR, stepping up to a more modern one may well offer some improvements in sound quality. I went from a low cost Onkyo as part of an old HTIB rig to my Marantz, using the same speakers from that box set up, and the sound quality change was subtle but noticeable.
The biggest change was in the signal processing and less distortion. That old subwoofer sounded new... I could run it hotter with less issues when it was connected to the Marantz.
So:
Speakers are usually where you go for sound quality.
Better subs will always be a significant aid.
But a new receiver may well be an improvement too.
Check out, for example, the Denon 3500 and 4500. Last years models available at a nice discount! Solid units by all accounts.
Careful planning and smart shopping can help you to a new rig. And good advice from friends here!