Yes really. In my 45 years experience. People have a tendency to spend the most money on their speakers. But you can’t expect them to perform their best with just any old amp.
What weaknesses do I think his current pre amp and amp have? Well I’m not here to put down anyone’s equipment, as I think that would be rude.
But what I will say is that it begins with the quality of the recording. Bad recordings on great speakers can be very disheartening.
Then you have the input device, and then pre amp and amp.
Amps, amp design, they all sound different. So yes, changing your amp can greatly change your sound. Especially going from an AVR to a dedicated Stereo amp.
Right now I have five different stereo amps, with the same set of speakers they all sound different. One sounds bright, ones warm, one has lacking soundstage.....
On the other hand, I have brought home a new set of JBL’s speakers only to realize, it sounds pretty much the same as what It was supposed to replace because the amp is the same. It’s not like I had bad speakers to begin with.... However, introducing a room correction system, possibly an equalizer, having a more powerful amp, a preamp with a really nice dac in it...... That will really change the sound!
Amps and DACs have changed since his 2013 model AVR, he might want to take advantage of that.
The speakers he has now are one of the most highly reviewed and awarded speakers at the 10K price point. I’m not just saying that because I own them. I’m say that because many famous and talent recording engineers use them in mastering/remastering many artists. Even if he spent another 10k on speakers, he wouldn’t get a noticeable difference in sound quality. These speakers handle 750 watts per channel, and driving them with power it really opens them up.