5 channel upgrade vs 2 channel upgrade

First time poster here. I am planning to buy a new amp in the next few weeks and did have my mind set on the Parasound A51. But then I saw the new A21+ Which appears to be a significant upgrade to this line, and read a very enthusiastic review. In general time with the system is split between Video and Audio so I’m struggling with whether it’s better to upgrade all 5 channels or really upgrade 2. My system consists of an Anthem MRX 520 Receiver, Blusound Node2 streamer, Rega P6 tt with Ania cartridge, Rega Aria phonostage, and Audio Monitor Gold speakers (200 fronts, 350 center, and FX rears).  I recently added a PS Audio P15 power plant. I did talk with folks from Parasound and was told there is no current plan to upgrade the A51. Any advice and/or opinions are appreciated.