amp or preamp to extend upper end


I went from a fantastic little Krell integrated amp to a Musical Fidelity M6 amp and preamp. Found that the high end is a bit rounded off -- that amazing detail I had on the cheaper Krell is lost. My dealer said that the owner of Musical Fidelity designs his equipment for this sonic signature intentionally. Maybe I just got to used to an over-emphasized high end.

Question: would replacing the amp or preamp have a more noticeable impact on extending the upper range (assuming the new equipment can do so)? Any suggestions? Speakers are Vanderteen 3s.
evolving
I have always found Vandersteens to be inherently a little soft sounding. Maybe the Krell was compensating for the top end of your speakers.
The MF stuff is clearly not doing everything you're looking for due to how it's voiced, so I'd dump both the pre and amp and start from scratch. Trying to mix n match to try to compensate seems like a potential exercise in frustration. Square peg round hole thing. From my experience Bryston gear does what you're looking for, or maybe go back to Krell. Best of luck.
Thanks folks.

I thought I was "upgrading" from my little old Krell integrated in going to the much more $ MF components. And they sounded pretty good at the dealer, but they were setup with a much more forward sounding speaker so probably not the best indicator of how they'd sound with my Vandersteens.

I may need to go back to what I know I like...Krell. But in the meantime will try your suggestions: check out Bryston, tweak the Vandersteens and look at resonance device.
Just a FWIW: brightness and detail are not the same thing, but quite often when an amplifier is bright, it is often perceived as more detailed.