has your current system ever really sounded to your tastes, like when you first got things together?
just for kicks, maybe you can borrow another amp and this time an SS amp briefly and see the diffs for yourself. just as an investigative step before throwing more $$$$ at the rig.
if indeed your amp is a solid mate in terms of current and impeadance a different preamp is likely not going to solve the issue
if you seek to attenuate or enhance certain sonic properties then a preamp may help. somewhat.
I would ensure first your amps IMP taps are set properly, 2, 4, 8 ohms etc as to the speakers nominal imp as best as your amp allows.
Iv’e had speakers that ran better on the 4 ohm tap, and some that ran better on the 8 ohm taps and both speakers sets were reputedly ‘6’ ohm nominal IMP according to the maker.
regardless where they are lower them to the next lower setting or raise them to the next higher setting and that will give you more insight to the situation.
just go real easy on the volume.
if that was a no go
I’d then look at rolling some tubes in the amp.
if you already have a tubed preamp then again, roll tubes there.
NEXT, I would try changing ICs, spkr cables, and or power cords thereafter.
THEN maybe if I were still dissatisfied with the highs and mids, I’d look at getting myself a different amp.
or at least one to just run the bass drivers.
power is a wildly used term here and its usual inference is aimed at drivability of what ever speakers. watts is what the makers give us in their opinions as their amps measuring stick for a general guide to matching them to speakers.
it takes current and or voltage to drive them essentially. if highs and mids are dull there may be a poor impeadance match upstream in the system. source to pre, pre to amp, or amp to speakers, or multiple mismatches. are present.
speaker makers as well give us their numbers for nominal IMP and so forth, and we are left up to find out for ourselves just how well our fav amp and fafv speaker like each other.
This connection reveals itself early on as to how well things willl be for the duration.
its a pityful case to expect things willl at some point changge from night to day suddenly from what we hear in break ins.
we can’t always go with what makers put on paper to match components properly.
sure hope things wind up the way you would prefer.