OP, FWIW, I think your goals in getting and setting up your system may be based on a misconception about what it’s all about. The goal is to set up a system that accurately reproduces the sounds as they are recorded by an engineer in a studio (or live for that matter). Recording wise you get just that. The recording engineer places the mic’s and puts down tracks for each mic. Then he mixes them to reproduce his recording. Then this gets put on a disc or tape, etc. Then you buy it take it home and play it on your system. He did not design/set up your system so is not responsible for what you actually hear. All very obvious, yes?
Now most of your recordings are not made by the same engineers, different engineers, different musical sounding recordings, even with the same music.
In a well matched and set up system you get to hear the recorded music exactly as it exists on the disc.
When I look at your original post I can’t begin to understand where you have heard that music, as recorded, and find such divergence in the sound made by the system depending on the type of music you are listening to. IMO if you set up your system so that you hear one type of music as you want it to sound, without regard to the actual music on the disc, you will alter the sound when you play different types of music, for better or worse.
I would suggest that you rethink your expectations of your systems performance based on its absolute audio performance not your present expectations of how it should sound with one particular type of music.
FWIW I doubt that the amp you have purchased (?) will solve your issues, hope that it does, just doubt it. FWIW, being able to match impedances is important but I don’t think that that issue alone will make the difference you seek. It can make a tonal change for sure and the 10K output of your preamp is unusually high yet resolve your audio issues, I doubt it.
Hope things work out for you.