Jafant, I would recommend an amp capable of a minimum of 300 Watts into 3 Ohms, and I would personally prefer double or more than that. The combination of a sub 3 Ohm minimum impedance and challenging phase angle is likely to make most tube amps less than comfortable. Thiel recommends at least 100 Watts per channel for the 2.4's. Bear in mind that recommendation is based upon quality ss amplification that can double down, and in this case almost double down again! If the amp can't double down as such then you'll need to increase the power output of the 8 Ohms rating accordingly. There is an old audiophile rule of thumb that I have found to be excellent guidance: buy at least twice the minimum power recommended. With speakers like your Thiels if using tubes double that again, and then again.
As for your apparent preference for an integrated over separates, there are some things that you might want to consider. While it's true that the case work and especially the face plates are amongst the most expensive parts of amps, so minimizing those costs would appear to value laden. And there is something to be said for shorter signal paths and the elimination of an extra set of interconnects that integrateds provide. On the other hand, I think you'll find that most intergrateds due to reduced size and corresponding heat sink real estate will have to run cooler than their separates counterparts. Very often that is accomplished by reducing the amount of Class A bias and the advantages that can come with that over the now increased Class AB output. Furthermore, you've probably noticed that many manufacturers top of the line pre's come with separate power supplies so as not to contaminate the delicate low level signals that pres work with. If these manufactures find the relatively small power supplies of pre-amps an offense, imagine what kind of insult power amplifiers might induce?
