Rogue Atlas Magnum sounds bright -- any recommendations?

Try changing the speaker taps and see if that helps!

I just changed the taps from 4 ohm to 8 ohm and the music sounds very thin.  With my 11 ohm speakers, I thought this might be helpful, but it is a move in the wrong direction.  It was worth trying. 

Call Rogue. They answer the phone and are extremely helpful.

I don't know if adding $4500 worthy of massless tweeters will do you good, but here are some tone controls, I found very effective. Please don't throw things at me for this.  I had a bright analytical system with tubes and Focal Electra speakers. I introduced Cardas ICs Golden somethings and it was like heaven.  Second I highly recommend rolling every tube I had KT-90s in a small amp and found them bright as well, use GL reissue KT77s.  Get every small signal tube that is Chinese or old Russian out.   Replace with NOS if possible or GL reissue (yes I know they are Russian but they are mellow).  Get the cables I kid you not they are now NOS or used but that makes them cheaper.

@mechans  +1. Everything I've ever read about the Cardas Golden cables indicates that they were well named.  I can't speak to the tube situation but what you recommend makes sense.

OP - Agree with @donjr  give Rogue a call.  No one knows their gear better than they do.