As others have mentioned, upgrading the amp without upgrading the preamp will only get you so far, and upgrading to separates will be pretty expensive. Given your investment in speakers, if it were me I'd upgrade to a higher level AVR so you upgrade both the amp and preamp in one shot. Anthem makes relatively high quality AVRs, so I'd look for something like this if it has the features you're looking for.
https://www.audiogon.com/listings/lis974j9-anthem-710-receiver-receivers
If you want to go further than that, I'd do a Marantz prepro with maybe Rotel or Classe multichannel amps, but it will cost a lot more and you'll need to add good interconnects. FWIW, and best of luck.
https://www.audiogon.com/listings/lis974j9-anthem-710-receiver-receivers
If you want to go further than that, I'd do a Marantz prepro with maybe Rotel or Classe multichannel amps, but it will cost a lot more and you'll need to add good interconnects. FWIW, and best of luck.