Amp vs preamp question

I have to agree with Mapman here. Especially with Thiel's. Thiel's are more demanding of appropriate, quality amplification than most speakers. BTW, I've been using Thiels for 20 years.

The Thiel 3.7's drop to 2.8 Ohms, very few tube amps are at their most comfortable operating into such a load.

Very few integrateds have the power, especially into sub 3 Ohm loads, to get the most out of the Thiels.

I have to (mostly) agree with Tvad, here. The 10 to 1 ratio is only a guideline and there are many respected voices that disagree. Though a bit off topic, other considerations re: pre to power amp matching include output and input sensitivity, the potential for DC leakage and how it is tolerated, and single ended vs. balanced operation. And let's not forget sonic synergy.
If one reads through the archives here on Audiogon, one will find that some are satified will fairly low powered amps on their Thiels, but more often than not, those who have tried various quality amplifiers, find that the higher powered ones work best. While the majority of music played doesn't usually require gobs of power, the balance can suck up huge amounts very rapidly. With the Thiel's, I think the cost of appropriate high quality ss amplification can be a bit dear and the cost of high powered tube amplification can quickly come cost prohibitive. SS amps seem to offer a better value with Thiels(!). IMHO, ss amps sound best when they are not run into their limits... with ss amps, having some headroom is advisable.
BTW, I certainly hope that Ledenhheim doesn't have an "18 X 18" room!

Without the "numbers" the quest might be endless and terribly expensive. The numbers don't neccssarily provide the ultimate answer, but they can sure get you there quicker. I'm in complete agreement with Tvad here.