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
In my experience, I have found that a pre and the amp each work best if they come from the same manufacturer. Sometimes if they aren't you can end up with surprises. The same manufacturer designs these things to work together..
06-06-15: Stringreen
In my experience, I have found that a pre and the amp each work best if they come from the same manufacturer. Sometimes if they aren't you can end up with surprises. The same manufacturer designs these things to work together..
From my experience, I find as long as the pre (low impedance) can drive the amp properly, it's a good match. They don't need to come from same manufacturer.
Atmasphere: I'm considering the MP-3 MKIII preamp. No experience with tub components, concerned about sacrificing detail and precision given what I've read about tubes from others. Any advice? Thanks. Paul
The MP-3 and MP-1 have direct-coupled outputs which allows them a lot of transparency and bandwidth. Detail is not a thing they are lacking. I find solid state to be bright but lacking detail by comparison.
Thanks to everyone for the feedback.

I found a really good deal on 3 month old Cary SLP-05 tube preamp. Very excited to hear it. I think this will be a great introduction to tubes.