Krell DUO 300 XD vs Krell Solo 575 XD


I am strongly considering this upgrade. I really don't need the extra power as I use a Martin Logan Balanced Force 212  sub which really bring impactful bass. What I am looking for is increased fidelity? Would appreciate any feedback. I love the  Krell XD amps!
bulldogger
I'm sure the upgrade would be noticeable. By increased fidelity, exactly what do you mean? What are you looking for, clarity, detail, noise floor, some kind of different sound?
Not just more power. Same sound. Love the sound. I wouldn’t want to upgrade to play louder. 
You are sure upgrading would be noticeable ? Any experience with amps

Question, what speakers are you using, ML model? Yes, I'm familiar with both Krells you mentioned. Very good amps, but only 40v/µs rise time. They don't have the "sparkle" of some other amps in their price range. I don't like the fans when they come on and you turn the volume down, audible.
I use McIntosh XR200 speakers. The 300 Duo XD is extremely dynamic with my speakers. Deep tight bass. I don’t hear fans from my seating location. Absolutely love the Krell sound. I’m not interested in other amps, just upgrading within this line.