Move from Parasound A23 to A21/A21+ or Something Else?

Hello, looking for some advice on an amplifier upgrade. Some years ago I was able to get an original Parasound A23 for a really great deal. I like the amp quite a bit and it was a wonderful upgrade from a class d amplifier I was using. I am mostly happy with the amp but I have noticed on loud or complex passages that the music can become strained sounding. It will shift from a nice layered and smooth sound to a more brittle and flat sound. It’s like the soundstage collapses to one dimension right between the speakers and music gains a hardness to it. It’s hard for me to explain exactly as I not that great at descriptors for audio.

Anyway, it doesn’t happen all the time only when listening to dynamic and busy music at higher volumes like 85+ db average at the listening position; about 3 meters from the speakers. The room is around 4500 cubic feet and semi open to other rooms. The speakers are Focal Kanta 2s. When I calculate the actual needs for wattage based upon distance and sensitivity, I "should" be fine with the A23. However, I wonder if a more powerful amp would help with the issue?

I like the signature of the Parasound so I am thinking of a used A21 or maybe even the A21+ if I could snag one at a good price. Is there anything else that should be on my radar? Looking to spend up to $3K max, less is better. Or, I could save up and maybe get a JC5 in 9-12 months if it was really worth it.

Open to thoughts and ideas.