@johnhh, Please note the following:
Thiel CS1.5 Owner's Information (Page 5 of 6) | ManualsLib
CAP-101 - Integrated Amplifier - Classé Audio Support (classeaudio.com)
Classé CAP-100 integrated amplifier Measurements | Stereophile.com
The CS 1.5's is a honey of a speaker for a small room. They still need to be, like the bigger models in the line up, placed somewhat out from surrounding walls and still be at least 8' from the listening position. As a design decision, that makes some academic sense, but I question the practicality of such placement requirements in the typical small spaces in which they will be used.
In any event, they should work quite nicely indeed in your smaller 12 X 15 room, but for the 24 X 24 room, a larger, even if older model Thiel might be more appropriate. In addition the power requirements might be quite different.
Note that the CS 1.5's drop to about 3 Ohms, while not brutal, still demanding. Not typically where intergrateds thrive. While there are a few very expensive exceptions, many intergrateds are not capable of doubling down with impedance like their separates counterparts. Additionally, intergrateds tend to drop their more linear Class A output bias into lower impedance loads at a faster rate than their separates counterparts. It is a mistake to assume that intergrateds are just compacted versions of their separates counterparts.
Thiel recommended quality amps rated between 50 and 150 Watts per channel into 8 Ohms for the CS 1.5's, with the understanding that these quality amps could double down into impedances. That would be about 150 to 450 Watts into the minimum 3 Ohm load of the Thiel CS 1.5's. It's not likely one will find a 3 Ohm ratings, but the amplifiers capable of doubling down into 2 Ohms will most likely make claim to it in their specs. If it's not there, they're probably not capable of it. To be safe; look for amps that have ratings of between 200 and 600 Watts into 2 Ohms. Room size and sound volume will ultimately determine power requirements. For the your small 12 X 15 room the lower power figures will probably suffice, but for your larger 24 X 24 room consideration, more power will probably be desired.
Though often promoted by dealers as a good match, the Classe' Cap 101 and Thiel CS 1.5's combination was probably more of a marketing match. After all, the more capable Classe' separates worked well with many of the larger Thiels. While the Classe' Cap 101 is within spitting distance of the minimum suggested power at close to the actual impedance load, we can see from the specs that it appears to be struggling to up power into a 4 Ohm load with just a 40% increase in power from 8 Ohms into 4 Ohms, instead of the desired 100% increase. I think it fair to assume that the expected power increase into the CS 1.5's 3 Ohm load the Cap 101 will be compromised. The above linked measurements of the earlier Classe' Cap 100 shows that it blew a fuse when delivering only 200 of the 400 Watts expected into 2 Ohms when driving only one channel. Put another way; a half the 8 Ohm rated Krell KSA 50* power amp will handle the CS 1.5 impedance load better. Don't be fooled into thinking you might be covered with a "stable into 2 Ohms" disclaimer. That only means the amp won't go into oscillation when presented with a 2 Ohm load. That could mean that the amp just shuts itself off before blowing up. It doesn't suggest how much power, at what linearity, with how much distortion, or how it will actually sound at 2 Ohms. In your 12 X 15 room you might get OK results, but should you want to use the 24 X 24 room you might find the Classe' CAP 101 wanting.
* Krell KSA-50 power amplifier Specifications | Stereophile.com
Thiel CS1.5 Owner's Information (Page 5 of 6) | ManualsLib
CAP-101 - Integrated Amplifier - Classé Audio Support (classeaudio.com)
Classé CAP-100 integrated amplifier Measurements | Stereophile.com
The CS 1.5's is a honey of a speaker for a small room. They still need to be, like the bigger models in the line up, placed somewhat out from surrounding walls and still be at least 8' from the listening position. As a design decision, that makes some academic sense, but I question the practicality of such placement requirements in the typical small spaces in which they will be used.
In any event, they should work quite nicely indeed in your smaller 12 X 15 room, but for the 24 X 24 room, a larger, even if older model Thiel might be more appropriate. In addition the power requirements might be quite different.
Note that the CS 1.5's drop to about 3 Ohms, while not brutal, still demanding. Not typically where intergrateds thrive. While there are a few very expensive exceptions, many intergrateds are not capable of doubling down with impedance like their separates counterparts. Additionally, intergrateds tend to drop their more linear Class A output bias into lower impedance loads at a faster rate than their separates counterparts. It is a mistake to assume that intergrateds are just compacted versions of their separates counterparts.
Thiel recommended quality amps rated between 50 and 150 Watts per channel into 8 Ohms for the CS 1.5's, with the understanding that these quality amps could double down into impedances. That would be about 150 to 450 Watts into the minimum 3 Ohm load of the Thiel CS 1.5's. It's not likely one will find a 3 Ohm ratings, but the amplifiers capable of doubling down into 2 Ohms will most likely make claim to it in their specs. If it's not there, they're probably not capable of it. To be safe; look for amps that have ratings of between 200 and 600 Watts into 2 Ohms. Room size and sound volume will ultimately determine power requirements. For the your small 12 X 15 room the lower power figures will probably suffice, but for your larger 24 X 24 room consideration, more power will probably be desired.
Though often promoted by dealers as a good match, the Classe' Cap 101 and Thiel CS 1.5's combination was probably more of a marketing match. After all, the more capable Classe' separates worked well with many of the larger Thiels. While the Classe' Cap 101 is within spitting distance of the minimum suggested power at close to the actual impedance load, we can see from the specs that it appears to be struggling to up power into a 4 Ohm load with just a 40% increase in power from 8 Ohms into 4 Ohms, instead of the desired 100% increase. I think it fair to assume that the expected power increase into the CS 1.5's 3 Ohm load the Cap 101 will be compromised. The above linked measurements of the earlier Classe' Cap 100 shows that it blew a fuse when delivering only 200 of the 400 Watts expected into 2 Ohms when driving only one channel. Put another way; a half the 8 Ohm rated Krell KSA 50* power amp will handle the CS 1.5 impedance load better. Don't be fooled into thinking you might be covered with a "stable into 2 Ohms" disclaimer. That only means the amp won't go into oscillation when presented with a 2 Ohm load. That could mean that the amp just shuts itself off before blowing up. It doesn't suggest how much power, at what linearity, with how much distortion, or how it will actually sound at 2 Ohms. In your 12 X 15 room you might get OK results, but should you want to use the 24 X 24 room you might find the Classe' CAP 101 wanting.
* Krell KSA-50 power amplifier Specifications | Stereophile.com