The P6/A21+ combination is an excellent combination. I enjoyed auditioning them. Can’t go wrong with Parasound. You might want to also look into the RC-1590/RB-1590 pairing from Rotel.
When I was looking to upgrade like yourself it was down to Parasound and Rotel. I ended up preferring Rotel. I perceived the Rotel being a bit more muscular and The Parasound a bit more laid back/polite.
Good luck in your search. Btw, the Arcam SA20 is fantastic. If your room isn’t too large and you can run the Arcam within it’s limits the MA speakers should sound pretty good with it.
Cheers,
Scott