I run my Ref 5s with a single MC275 Mk VI with upgraded tubes. I was going to add a second to run them in mono but didn't feel the need for it (my room is about the same size as yours). Some say that the Reference line really needs high watt amps to shine, but I really like how mine sound now running with an all tube front end.
If you want to try at a lower price point first, I would say that either Rogue Audio Atlas Magnum or a used PrimaLuna Dialogue Premium HP would be a good place to start. If you felt the need to upgrade (but you might not after hearing either of these in your system), you could most likely resell them with minimal financial exposure.
If you want to try at a lower price point first, I would say that either Rogue Audio Atlas Magnum or a used PrimaLuna Dialogue Premium HP would be a good place to start. If you felt the need to upgrade (but you might not after hearing either of these in your system), you could most likely resell them with minimal financial exposure.