Well, I made the switch way back in ’94 in the oldy but moldy days of Dolby Prologic, and the AVR I had been using was a JVC (I forget which model). What I switched over to was a B&K HT digital preamp, a Cary SLA 70 Signature (amp) for the left and right speakers, a 30 wpc Rotel amp (I cannot remember the model, but later I guess I can check) for the rear speakers, and an identical Rotel amp, but in bridged mono, for the center channel speaker. At the time I was listening to a Carver CDP.
This was over 30 years ago, but as I remember the main improvement was not in the HT experience, but listening to CDs was more enjoyable. I don’t even do HT anymore as sometime in the later ’90s all my upgrades went into my two channel system.