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
Why did you go away from the Krell? Is there compelling attributes of the new gear that make it overall superior?
You might want to try a Schumann Resonance device such as the Acoustic Revive RR-777 or the Kemp SR-Plug. I am amazed at how effective these tweaks can be in enhancing the detail and dynamics of even a very good system. Do a search on Audiogon to see that there is already a considerable amount of discussion on this topic.