Moving to separates

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.

I have the following integrated amp replacement stack from Schitt Audio in my office. It is my second best system.

Schiit Audio: Audio Products Made in USA

My DAC is the Schitt Yggi+ OG, but I would get the lower cost DAC offered in the Gigastack package since it is also very good. I also got the Kara F preamp and had the Freya+ previously. I like the Kara F more.

It is as good as the following gear I had previously (maybe a bit better and more features for sure)

- 8k amp, 9k amp, 7k preamp, 15k DAC and streamer, 8k integrated amp 7k integrated amp

The Wotan amp is one of the most powerful amps I have owned. It needed about 2 months of heavy play to sound as good as it does now.

You also get a 15-day home trial period to hear it before you commit. Though the amp and DAC will need more time to sound their best.

I have considered an integrated amp to replace my separates, with which I am happy (incl an Odyssey Khartago++ amp). Why? Amp/preamp synergy in one box, eliminating interconnects. Two are on my short list because they "play well" with my Vandersteen Treo CT speakers:

1 - Aesthetix Mimas

2 - Ayre AX-5 / Twenty

3 - A few others including Constellation and Soulution, which are quite a bit more expensive and therefore out of reach, though excellent.

I like the idea of simplifying my system to just an integrated plus DAC (maybe even internally...Aesthetix does a good DAC card), and streamer and CD player.

OR— I will got the other way and get monoblocks! Oy. Choices, choices.