I added an amp to my h/k AVR-7000. That receiver is ALL amp. It's known for the amp and that's about it. It was h/k's flagship for good reason.
I added the Sherwood Newcastle AM-9080 amp and the difference is huge. I'm currently in an equipment flux and have the amp disconnected (receiver...
My experience with adding an amp to a receiver was the opposite. I thought I got a whole new system -the difference was that obvious.
List your budget and these guys will chip in with a ton of suggestions.