I have a pair of 3.6s and have had good results driving them with solid state amps of 100 watts per channel or more. The 3.6s (and 3.5s, I believe) are difficult to drive with an impedance curve that dips below 3 ohms at points. I understand that the audible effect is often flabby or weak bass with low to moderate wattage tube amps. (Implicitly, a high wattage tube amp might be fine.) They can be a pretty good sounding speaker, especially with solid state amps that can pump out the current. Good luck.
