The 3.5 goes deeper in the bass region, but the bass is a bit limited in SPL output. The 3.5's has a much easier impedance load. The 3.5's eq augments the natural roll off of the woofer. As such it makes demands on the amp. This is somewhat offset by the fact that the impedance load become gradualy higher as the eq's power increase demands. The eq does offer two levels of bass boost to accomdate different size rooms. The sealed box of the 3.5's allows for better time and phase intergration. The 3.5's midrange driver surrounds can fail, but, Thiel's customer support is second to none and can be counted on to provide terrific support.
The 3.6's don't go as low, but offer greater SPL's. The 3.6's demonstrate a notably smoother mid to high frequency response.
Both benefit greatly from high quality, high powered amps. You can get by with some(!) budget gear, but you'll never hear what they're truly capable without the appropiate amplification. Unless you have a very high amplifier budget, top quality ss amplification is recommended. If you can't afford to power them properly, perhaps other speakers should be considered. The 3.5's are more fussy with regard to the mid to high frequencies, but 3.6's impedance load is more demanding.
FWIW, though I might be in the minority, and despite the 3.6's obvious advantages in some areas, I prefer the 3.5's.
At the current asking prices the 3.5's might be one of the best baragins in all of audio. Just bear in mind that, both, and perhaps especially in the case of the 3.5's, break from my and many others typical advise, in that to get them to work at their best, you might need to spend more on amplification than on the speakers to maximize the total systems sound.
The 3.6's don't go as low, but offer greater SPL's. The 3.6's demonstrate a notably smoother mid to high frequency response.
Both benefit greatly from high quality, high powered amps. You can get by with some(!) budget gear, but you'll never hear what they're truly capable without the appropiate amplification. Unless you have a very high amplifier budget, top quality ss amplification is recommended. If you can't afford to power them properly, perhaps other speakers should be considered. The 3.5's are more fussy with regard to the mid to high frequencies, but 3.6's impedance load is more demanding.
FWIW, though I might be in the minority, and despite the 3.6's obvious advantages in some areas, I prefer the 3.5's.
At the current asking prices the 3.5's might be one of the best baragins in all of audio. Just bear in mind that, both, and perhaps especially in the case of the 3.5's, break from my and many others typical advise, in that to get them to work at their best, you might need to spend more on amplification than on the speakers to maximize the total systems sound.