Inherently yes a tube preamp will allow for some lessening of top end energy as a rule, although Id say dont let that scare or annoy you, as this effect is by degrees primarily and usually not night and day sorts of differences.
The rule of thumb Ive discerned so far on the affect of a tube preamp is that they afford a greater ease to the receipt of the sound itself. Better decays, and more harmonic resonance.
This affectation can be either very great or simply noticeable. And theres the rub for some. Its not extremely promising of any exact outcome, offering more so mere vague notions which while in ones mind can become magnified without due cause and wind up as offputting.
And there too is the lure of tubes in the power train, simple pure end user flexibility. The ability to amend or attenuate the signal without degrading it just by exchanging tubes within its company.
In the most generic of ways, people say rolled off when speaking of tubes, generally. Its not correct IMHO. The bite can and often is reduced from the usual overemphasis of most rock & pop recordings when the application of a well designed tube device is on the job.
I feel a better terminology would be to say the highs are made more natural. Of course this variable concerns itself with just how good a tube this or a tube that is in the system mix. To some degree too, those tubes within it as well. Adding a nice tube pre with very dynamic and extended tubes in its compliment isnt going to provide quite so much change, as if its compliment of tubes were rolled towards a smoother sort instead.
I know some SS preamps which sound quite different from their own amplifier counterparts too. Krell for example has some very dynamic amps, but their preamps arent quite so aggressive. Id assume other makers could take that approach too.
A very good post was made here above regarding the type of music you will listen too going forward and the choice of preamp for it/them if rock and pop are your bread and butter, and all else is disinteresting and likely will remain just that way, go with SS preamps. Theyll cost you less money than tubed preamps will and youll have all the extension and speed those genres require.
Back when I was considering adding a SS preamp simply for another take on the music and as a backup only, a friend here mentioned to me the Rowland Capri. They arent way pricey and resell quickly. Past that Id consider Levinson or McIntosh, as Ive heard some from both of those makers SS units.
With that BAT amp Id first think of looking around for a good 51SE too. I know of a couple friends who own those and their accounts to me on them dont show them up as your more harmonically rich and somewhat slower paced tube preamps but youll also find that as the price goes up on tube preamps, so too will all the other audio nut agendas PRAT, extension, inner detail, etc. And its a 100% balanced design with that inherenet synergy of the BAT sound!
Again, FYI, there are tube preamps out there today which when eyes are closed, are very difficult to tell from SS preamps. Ive never understood the why of that prospect though, aside from many have been intended for use in some HT rigs as they have the HT bypass option built into them as std.
Have fun