Prilaluna Prologue Premium with KEF LS50

Hello all!
I just purchased a used PrimaLuna Prologue Premium with stock tubes. It replaced a Sophia Electric Baby amp. The Primaluna seems to have a peaky upper midrange I can't seem to tame. I doesn't seem like I can see inside the music like with the Sophia. For example if a flute player takes a breath I can't hear it as well. I have tried cables with no luck. Any help?
Thanks in advance.
Ben