Audio Research pre-amps?

The ARC LS3 is a solid state preamp. Almost any tube preamp,
(whether ARC or not) will add a touch or more of warmth and
soften up the brightness.

Its true a good tube pre-amp should be a step in the direction of more warmth and perhaps less brightness, but that alone is not a guarantee.

I use an ARC sp16 in front of the Triangle Titus speakers that I have had brightness issues with those speakers (not others off same rig) in some rooms/cases even with the tube pre-amp.

The sp16 is quite detailed and only the slightest bit warm to the point of making it hard to distinguish as a tube device compared to other good SS gear.

Other tube pre-amps likely tend towards a warmer tube like sound, but not the ARC sp16. ARC in general is known more for factors other than "warmth" I would say.

I am not a fan of the unnatural coloration too much warmth adds to certain recordings in certain genres in particular.

The best SS and tube gear tend to sound similar IMHO and not overtly warm, nor bright either, with the right setup to go along with it. ARC gear in general (VAC also) seems to reside firmly in that camp, especially in comparison to some other tube gear I have heard.

I will second Mapman's suggestion. I also have an ARC SP-16 which I use with a pair of Quicksilver Midmonos to drive Monitor audio RS-6 speakers.

I agree the SP-16 does not sound overly warm but does take the edge off the highs.

Might not be the ARC or any other piece of gear.Have you tried looking at the room and the treatment if any?

I've owned several ARC preamps, tube and hybrid designs, though I've never owned a SS ARC. I found all of them a touch too bright for my tastes. I would recommend looking for a VAC preamp in your price range. I found VAC to be almost as revealing as ARC preamps, but with just a hint of sweetness. As always, YMMV.