How do tube Watts compare to SS Watts?

I have Theil 2.2 speakers, which have a low sensitivity (86dB), but I would like to get an intergrated tube amp. Or even all tube. But I don't know how many tube Watts I'll need to drive the Theils. My guesstimate is @ 50wpc for intergrated tube amps, but that could be wildly off. Are their mathematical conversion formulas? Second, if there is a rough range, might you be kind enough to suggest a few worthy candidates that, wheather new or pre-listened, are under $1,000 USD (e.g., Cayin model xxx). Thank you most kindly.
In my experience tubes and Thiels are a very good match you just need enough tube power to drive them and there are many factors that determine power requirements. Thiels are a demanding load but not difficult one because of the relatively low but flat impedence curve.

Depends on the tube. SET amps with 300B, 845 are low power, "no slam" "no authority", but a midrange and highs to die for, WITH THE RIGHT SPEAKER. So scratch those off my list. ...KT88's. I heard one cheap chinese 88 and also rolled 88's in my JOR. Absoluetly no authority. Very very weak on any speaker with 90db or lower. I havea Jadis DEFY sitting on my floor waiting for a preamp, has the 6550 tube. Very very nice looking tube and should be an improvement over my KT90 Jadis OR. The seller told me has "magic". Then there is the EL34, which doesn't look too interesting. Looks like a cheap KT90. There are other SET tubes like the 2A3 (ck name?), same issues as the 300 and 845. There are a few other tubes, but these are the most used in designs. Comes down to speaker first, then amp. So only the "beefy" KT90 does the job. I'm expecting the 6550 to come through as well. These are push/pull tubes. Sorry ss amps are not "my cup of tea". None.
I had trouble driving CS2's with Quicksilver mono amps that were rated at 60 wpc. The room was about 12 x 20 and I thought I needed tubes to make the Thiel's sound smooth and sweet but when I switched to a smaller high current SS amp they were controlled, not sloppy.

Best advice I can give is try a tube amp with some guts and use the 4 ohm taps if it has them. Or get a SS that doubles into 4 ohms.
Watts are watts. Tubes sound better than SS when they clip and its more subtractive. SS just sounds crappy when they clip.

Some manufacturers of solid-state amps have taken this into account. Levinson amps, for example, have a built-in smoothing circuit that eliminate this harsh clipping sound when the signal gets close to the supply rails. Another that comes to mind is McIntosh, whose PowerGuard circuitry has received acclaim as an effective mean to end hard clipping.

As for the Watts question, in theory it shouldn't really matter if the amplifier is tube or solid-state, because strictly speaking 1 Watt = 1 Volt x 1 Amp. In practice, the specification is approximate, so you can expect an amp with a bigger power supply and lower impedance to sound louder with the Thiels. Also, all amplifiers differ in their "power margin" above its nominal power, depending on their circuitry details.

As a general rule, 100 Watts per channel would be a good starting point to choose an amp for the Thiels. If the brand is serious it will correctly specify its product, so you shouldn't find differences of more than 1 o 2 dB in acoustical output between a solid-state amp and a tube amp in this particular case.
My jadis OR with KT90's will drive your speaker. Used, $1500. Also look at the Ming Da tube amp with KT90's/new at $900. The Cayin KT88 "might" work. But I surmise it may be a tad on the soft side. There's not many tube amps used under $1K that will offer "slam". 2 imporant factors that go into makinga great tube amp that has "punch" is the quality of trans and the quality of tubes. Neither of which come cheap. ....There are ss amps under 41K that will give some authority, but as far as fatigue factor and lack of musicality, I couldn't live with it.