Both are highly regarded brands and offer a variety of models.
Personally, if you're looking at a new amp in the near future -- especially if it's a tube amp -- I'd decide on that first before buying any speakers. The amp you choose could change everything and you may regret your speaker choice later. But given that...
I certainly understand the appeal of a tower speaker with powered bass versus using subs, but my concern would be there are so few options that might meet your requirements that you may be greatly limiting your choices and may not find something that sounds optimal to you.
Using a sub is obviously a less elegant solution, but the obvious benefit is that you’ll have many more speaker options that will work with your amp and may appeal more to your particular tastes. Also, with proper and likely better bass integration with your room you’ll likely end up with both significantly better and deeper bass with a sub (or even better, 2 subs) than you had before. With a budget of $10k you could get really nice monitors (or smaller floorstanders) and one or even two very good subs resulting in true full-range sound that meets with your personal tastes as well.
All that said, I’d also definitely check out Coincident Technology and specifically their Super or Total Victory models. They don’t have powered subs, but they are designed to be highly efficient/tube friendly and appear to go as low as your MLs (at least on paper). Great speakers that might meet all your needs if they sound good to you.
Obviously you could also bi-amp other paaive floorstanders with a SS amp driving the bass, and that might be a great option too but I really am not familiar with which speakers would work well with that. I'd be concerned about a potential mismatch in sonic character using the two radically different amps unless the speaker was specifically designed for that purpose, but that's just my personal neurosis speaking so take with big grain of salt.
Hope me this helps, and best of luck!
Golden ear Triton One or Triton Reference. Triton one are 92 db efficient and Triton Reference are 93 1/2 db efficient. Triton Reference has a 1800 watt class D subwoofer amp, and Triton One has a 1600 watt class D amp. Both have 3 powered woofers with plenty of very high quality bass and both have a level control to dial in the amount of bass wanted.
Good idea regarding the LM 518ia. I would give serious consideration to the LM 508ia amplifier. For not much more money it is a 48 Watt SET so operation is pure class A (as are all SETs). What’s very unique is it uses the 300b as the driver tube which is a DHT (Directly heated triode) for the 805 output tube. So you have a DHT driving a DHT. Owners of this amplifier who have posted on this site say the sound quality is simply superb. The 508ia is said to be a step above the already very good sounding 518ia which is 845 output tube driven by 6L6/6V6/el34 or KT 88 tubes. The 508ia is sonically comparable to the higher cost 219ia which also has 300b driver tube for an 845 output tube.
Charles 1 dad's suggestion of the Rethm speakers is interesting. I heard one of their speakers not too long ago and it was quite nice sounding, particularly for the money. I believe it had a built in powered woofer and utilized a full-range driver to handle everything from the upper bass on up. It is efficient enough to work with a SET amp for the full-range part of the system.
At a much higher price, the truly full-range Charney speakers are quite interesting. I heard them operating as a one driver, full-range system (no subwoofer), but, I think a subwoofer that came in at a fairly low frequency would help that system. It was also quite efficient too.
With the LM amp you should consider the Tekton Double Impact SE speakers. They cost $6500 new. They are highly effecient and offer tremendous bass. No powered sub needed in these. The LM would be a wonderful match. The bass in these speakers is as good as powered subs without the added electronics, complexity and cost. Tube watts (20-48) will rattle your room and thump your check with these speakers.
The Charney Audio Companion with the Omega RS7 driver would be a great way to go for your room size. I have listened to them in a 14x19x9 room and the bass is sufficient. You can always add one down the road if desired. Your choice of the LM 518a is far and away enough power. The RS7 driver lends itself well to low watt SET amps as well as SS amplification. I have a pair and listen in my 11x15x8 room. I currently us a pair of ANK interstage mono's, but recently demoed the Digital Amplifier Company Stereo Maraschino (STM) integrated. It gave my 300b a serious run for the money and is less than a quarter of the cost. A very good integrated I could easily live with had I not owned the ANK monos.
Enjoy your journey.
@larryi Yeah I've been hearing good things on the Rethm speakers. I particularly like how they designed the Bhaava. It's really nice to see a fresh take on what a speaker should look like. The idea of using a full range driver for its entire range and then a sub to prop up bass impact seems like a great idea. I hear Voxativ is coming out with something similar in the near future.
@chrisallen I to have owned a number of Omega Speakers and agree with you about the drivers in a box cabinet. That said the tractrix designed Charney horns take the RS7 driver to another level. Very close to the Lowther drivers Charney offers but with a slightly warmer tone. This horn design offers plenty of punch with involving micro and macro dynamics. If you get a chance audition them, you'll be glad you did.
Voxativ already has several models that feature an active (powered) woofer coupled to wide-range drivers. I haven't heard their speaker systems, but, I have heard a number of different systems utilizing their drivers. The sound of these systems varied widely; clearly implementation plays a big role.
The Charney speaker I mentioned above used a Voxativ full-range driver. Charney offers a choice of drivers. For my taste, the Charney with the Voxativ driver does not need a subwoofer. The sound was full and had plenty of bass. If anything, what I would want is a little bit more extension on top. That is a somewhat strange thing to say because sound a bit harsh and have a prominent peak in the treble range that makes one want "less" on top. This speaker was quite different from the typical single driver experience.
Voxativ offers the Zeth B and the 9.87 system which both include a powdered subwoofer. I’m quite certain that these are more expensive than the Rethm alternatives.
If I weren’t so happy with my current system I would acquire the LM 508ia (or a used Viva Solista) and Tekton Double Impact SE and not look back.