Problem with Rogue Medusa Amp (I need advice)

Hello fellow Audiogoners,
I recently upgraded from a Rogue Pharaoh integrated amp to a Rogue Medusa amplifier. My older MFA Magus tube preamp ended up sounding better than the preamp that is in the Pharaoh, so I ended running the Magus through the Unity Gain input on the Pharaoh and only using the amp section. I was happy with the sound of this setup, but decided that I could improve the sound by getting a Medusa amp to replace the Pharaoh integrated amp.

I am now running the MFA Magus preamp through the Rogue Medusa, but am having a problem with how the Medusa sounds. In every recording, LP or CD, that I play there is an unpleasant emphasis in the mid and high treble range during the intial attack of a musical phrase. It is an emphasis that is glaring a bit harsh and it makes my listening experience fatiguing and unenjoyable. Overall the Medusa has more depth, low end, and is more revealing than the Pharoah, but it is really unlistenable the way it is. 

I have tried three different sets of tubes with this amp, the original JJ tubes, vintage RCA tubes and Tungstrum tubes; all producing the same problem. So, I am wondering if I need to find better matching tubes for the amp to get rid of this problem, or if something in the amp has gone bad and I need to send it to Rogue for inspection. Has anyone had this problem with their Medusa amp? Please advise. Thanks!