Equipment does not match

Actually, that looks to be a pretty well matched system that should perform quite well.

The Rotel amp would seem to be a pretty good match for the speakers. The ARC tube preamp woudl also seem to be a good pairing. WHat is the input impedance of the Rotel? If less than 30000 kohm it might not be the best match for a tube pre-amp, but should still sound pretty good in that setup.

Whenever tubes are involved and sound heads south, always check and make sure the tubes are good and performing as they should. Either keep good spares to swap in and out to see which work best. Have the tubes tested if possible.

Next I would suggest confirming if speaker placement might be tweaked for better results.

Some more detail on what does not sound right exactly would help.

I've heard modern AMT type tweeters recently in Goldenear Aon3 speakers off Rotel class gear compared to other speakers/tweeters a/b. The GOldenears were the most "polite" in teh high frequencies actually. Some will find that nice but some used to more oonventional tweeters like soft domes for example might miss some of the "bite" that other tweeters may be more prone to. Dynaudio Esotar tweeters are a good example I think.

Have you tried placing a rug in front of teh speakers at the
main reflection point to where you liten from? Bare marble
floors sound like something that might benefit from a bit of
acoustic treatment. If bare walls also, an acoustic panel
on each side wall at main reflection point to your listening
position might be worth a try.

Also before that, sound like speakers might be too close to
the walls for best results.

The Sereophile reviewers positioned them 5' from the front
wall:

"I positioned the Burmester B25s 5' from the front wall, 6'
apart (measured from the tweeter centers), and toed-in 45°
to focus on my listening chair 7' away."

I'd play with the placement aways from walls a bit for good
soundstage and imaging and then perhaps try floor and/or
wall treatments from there as needed. Maybe try the toe in
as well. definitely get speaker placement optimized
before anything else.