Thank you! I have been in two car audio for decades now and have class D amps in there knowing they are the best for bass
Frequencies go way past audio range. Amplifiers are about electrical signals, not just audio-range electrical signals. Ever hear of a Class C amp? No? Because it's a high-frequency amp used for radio.
I bring this up because Class D is a low-frequency amp. But what is "low"? Well, that depends on the speed of the switching mechanism in the Class D. The faster that is, the higher the frequency class D can put out correctly.
If you wonder whether switches have been getting faster over the years: I'll tell you they are a limiting factor in network speeds as well.. how has your phone/internet data speed progressed over the last decade or three?
but as far as home theater, I've always had a surround sound system but never really concentrated on higher quality then just an over the counter thousand dollar Yamaha AVR
The quality on an Yamaha AVR is excellent. The limitation is usually around maximum current/power.
if that calls for me saving up a little more money to buy separates if it's that huge of a difference, then I will but if I can get by being an average user with high-end taste, maybe I can get somebody's and put on a really nice AVR and call it a day.
Get an AVR with pre-amp outs. I just picked up a new Onkyo 11.2 with pre-outs for <$500.
Your sub, the biggest consumer of power, is likely already running on its own amp. If you really want, you can externally amp your LCR both giving them more juice and reducing the overall load on your AVR for powering the other speakers.