The best tube amp I have heard for bass extension in a panel speaker was the Air Tight ATM-2. It has a very conservative rating of 80wpc and several have appeared here on Audiogon for sale this year. I had the pleasure of listening to this amp drive a pair of Sound Labs U-1s and it was stunning.
Most people recommend the opposite of what you are doing, tube pre / ss amp, for reasons you suggest ; that being bass control. I use a CJ 16ls II tubed pre-amp and CJ MF2500 ss power amp and find it to be a very good combination. Also tubes in pre-amps tend to last longer and are cheaper to replace than power amps. Just my thoughts.
I just bought a pair of Wright Audio 2A3 monoblocks (3.5 watts), and they have absolutely incredible bass response. Fast, tight, accurate. Of course you need efficient speakers with amps this small, but don't be fooled about bass response in tube amps.
Agreed with Czbbcl on the tube preamp/SSamp combo.
The maggies need lots of power.
Before you switch to a planer speaker, you should check
out some quality 2-way speakers, like the Talon Ravens
and the Wilson Benesch Arc.
Wolcott period bass every bit as good as any solid state amplifier you care to name.
I'm currently horizontally bi-amping a pair of ML Prodigy speakers with two ARC VT100IIIs. I was originally thinking about using a D400II to vertically bi-amp and drive the bottom end, but the bass I get is pretty tight as it stands...
I'm driving Magnepan 3.6's with a McIntosh 2102 tube amplifier and getting results results that I like a lot.
Magneplanars and SoundLabs are both panel speakers, but different types - Maggies, as their name suggests, are planar magnetics, while SL's are electrostatics. (If you are unsure what the preceeding exactly means, yes there are previous threads to search on this topic.)
Anyway, what this implies for amp selection (beyond the normal fact that different speakers will of course sound different from one another, and therefore will potentially have different system matching requirements from a sonic standpoint, including amplifiers) is that the speakers' electrical properties are not the same: Planar magnetics show a very flat, resistive load, while electrostatics present a capacitive load that slopes downward to very low values with increasing frequency. So without going overboard here, the two speaker types make different demands on a partnering amp, which might not be met best by the same design for both kinds of speakers.
Having said that, what is generally true of all panel speakers is that they are only moderately efficient, so whatever type of amp is used, it can't be really low-powered if you want to play at near-realistic volumes in any but the smallest rooms (and panel speakers don't work well in small rooms anyway, due to their dipolar radiation pattern, so some power will be needed).
As for tube amps, a common pairing with electrostats is OTL (output transformer-less) amps, partly because they can put out increasing power with increasing speaker impedance, something 'stats exhibit where the power is needed - in the bass range. Whatever amp is used with a 'stat will have to be stable into a highly capacitive load through the treble. Maggies, with their lower impedance in the bass range, are usually paired with output transformer-coupled designs if going the tube route, but amp instability should never be a problem with their purely resistive load. A lot of folks feel that it takes a very high-powered tube amp, however, to compete with SS when it comes to supplying Maggies with sufficient current to really bring them to life (electrostats are primarily voltage-driven, making them more compatible with medium-powered tube amps).
These are just generalizations though, and other combinations are possible. While I lack the experience to make specific recommendations, you might want to bring your question to the attention of member Audiokinesis if he doesn't find your thread on his own.
Judit, if you listen to classical music as much as I do you'll want to look at my "Midrange Electrostic System" under my moniker ivanj. The big advantage you have over me is you have the Pass X-1; presently I have to settle for the Pass-designed Adcom. Seriously, the Wolcotts are a final purchase for either the Mags or the SLs.
I think you are getting good advise regarding final speaker selection. I believe your preamp might sound best from it's balanced outputs. I'm not sure how critical this is in the big picture, but you might want to consider maximizing the sound of the units you already own and seem to be working around. You may find it challanging to find a tube amp that meets all your requirements and also has true balanced inputs. Good luck.
To expound a bit on your last two questions:
1) "Will I be able to get tight bass [with a tube amp], or will there always be a trade-off here?"
Strictly in regards to 'tightness', and also to 'slam', tube amps cannot, in my experience, quite go where SS can in the bass. This is a separate question though, from which kind of bass sounds most natural musically speaking. I haven't heard the leading contenders for bass in either camp, but what I have heard I've preferred the presentation in the bass of the tube amps (as indeed I have through the rest of the range when it comes to other qualities I value more highly, such as tonality of harmonic structure and a feeling of 'liveness').
2) "I would love to have a better technical understanding of the differences between the ways SS and tubes provide headroom."
Just technically speaking, the usual description of the difference here is that SS amps clip suddenly while tube amps approach clipping progressively, and that the distortion products produced are more benign in the case of tubes. Personally, I have always been somewhat dissatisfied with these assumptions, while true as far as they go, as a good reason for explaining why it is that tube amps often 'sound more powerful' for their given output rating than do SS amps. I have found that I cannot abide listening to either kind of amp at or near clipping, so the argument that tubes clip more pleasantly doesn't cut much ice for me (it's an entirely different story when it comes to electric guitar amps, but as a player myself, I can tell you that there is not to my mind any valid parallel between the two applications). I also am not persuaded by the fact that tube amps do not clip all at once like SS amps do, since if one stays below the clipping threshold, this means that SS will remain cleaner anyhwhere below a full-on clip than will tubes - something which to me would seem to imply a greater degree of aural comfort closer to the limits with SS. There is truth to the notion, however, that a clipped tube amp will be less dangerous to the continued health of one's tweeters than will a clipped SS amp, and that it's easier with tubes to tell when the limit is being approached without going over. I have encountered some arguments as to the apparent differences in headroom quality having to do with the fact that tube amps are run at much higher voltages than are SS amps, but I lack the technical understanding to assimilate the exact reasons for this, if true. You might want to direct this question to the attention of member Sean.
I presently own a pair of Eminent Technology LFTVI speakers which use linear field transducers. I have found them to be excellent overall and probably the best "ribbon" technology speakers I have heard to date for classical music.
My power amps (I have two) are older, upgraded Counterpoint NPS400's built by Michael Elliott (he can be contacted at altavistaaudio.com and is very experienced in circuit design) some time ago.
I believe that part of what you are experiencing is this: ribbon, or electrostatic speakers are notoriously inefficient, so you need to have a power amp with a high capacity. I had experienced problems similar to yours for a while, until I got hold of these power amps. They have a rating of 400 watts per side, and now that I have bi-amped the speakers, they sound incredible. (Bi-amping actually raises the output to about 650-700 watts.) I recently purchased a set of Mozart Symphonies performed on period instruments (the English Concert conduceted by Trevor Pinnock on the Archiv label) and the clarity is astonishing.
Hope this is of some help.
Waldhorn, just to be clear (since there has been confusion about this before, even in this thread), the "Linear Field Transducer" used by Eminent Tech is their name for a planar-magnetic driver, similar to what is used in Magnepans (we can defer to Magnepan about the naming of the technology, since they invented it). The "linear" part of this designation is a reference to the fact that their design is driven by magnets placed both behind and in front of the panel diaphragm (unlike some Maggie designs that have been driven from only one side.) The LFT-VI speakers use neither ribbons (unlike some Maggies' tweeters, or the late lamented Apogees), nor are they electrostatics (as are say, Martin-Logans or SoundLabs), terms used in your post. But you are right in saying that many panel speakers of any type tend to be somewhat inefficient in their need for amp power (although the fact that many such speakers are configured as vertical line-source radiators will partly ameliorate this inefficiency from an acoustical point of view in the listening room).