The MacIntosh preamp may have the balancing effect you are hoping for. Tell us what happens.
Don't forget that a new solid state amp typically starts out very trebly and then softens over the first 100 to 200 hours.
I know this, but I just can't help but draw conclusions when I put a new amp in my system, even after knowing this for decades. I get all upset... then it settles down. This happened to me recently... and it settled down so much, it was as if it was a completely different amp.