Moving to separates

I'd suggest getting out and listening to few systems either through local shops or audio members. If you arent sure if you would be able to tell the difference the first thing you need are a few good reference points. Otherwise you might spend significant money for gains that you might not even care about hearing.

Good luck and have fun.

My first system growing up was separates.  A few years ago, I thought about going the other way and I bought a Hegel H390 and it really sounded good, but I went back to separates just a couple years later.   I changed for a change in the second and no other reason.  I guess I’ll reinstall the Hegel this weekend and double triple check.

first off find a high end dealer that can "loan" you a few amp's to try in your system. I didn't see where you mentioned your budget, nor what you wish to improve. Here on Audiogon, The Music Room, etc. you can find a variety of used power amplifiers (two or three or five or seven channels) that can add to your listening experience. Do your front speakers allow for bi-wiring/bi-amping? What is their impedence curve? Most A/V receivers don't double the power into lower ohms, so if the speakers go into lower 6 ohm or 4 ohm territory, a power amp that doubles from 8 to 4 ohms will definitely sound better than the current setup. There are many variables, but if you are looking for "oomph" and bass slam I personally can recommend Krell & Aragon. Krell make some nice A/V style amps that are less in the A/AB power output than their bigger amps, but can still drive lower impedence speakers. Have fun looking for the next improvement to you system, and be sure to listen to it with your normal music.

the most expensive and subject to the most cost cutting will be the power amp section. Typically the power supply is a very large transformer (high cost), several very large energy storing capacitors.  heat sinks, power transistors.

Receivers/avrs are very cost effective in terms of functionality provided, but cost cutting will occur in the power amp section. The cost cutting would manifest itself as the amp not delivering the current required to meet output specks. Most loadspeakers hit a low impedance somewhere near 100 hz, Thus this would result in your 100 wpc delivering say  20 watts. It would be noriceable,

Take the preamp out to a decent 200 or more wpc  amp and you may here a substantial difference, dependent upom the speakers.

Thus when people say that speakers are the most important to upgrade, there is an asterisk that should say “dependent upon power amp specs.

Love this topic!  Over last 30 years I went from a 5 channel Sony consumer to a 7 channel Arcam receiver with Sonus Fbr Conerto surround spkrs system to to a 9 channel Onkyo consumer because the Arcam kept breaking.  Then to a Parasound Halo A5 with P7 pre, then added a Marantz AV 8805. Then upgraded cables to mid grade and now the Surround is complete and any upgrades are not worth the cost to me.  It sounds awesome with movies and pretty good with music.  A serious 2 channel is my next step in a separate room with separates.  No technical data here, just 56 yrs of listening to music.