Thiel Owners

tmsrdg,
This is an old memory so forgive any misstatements. 
I remember talking to Jim and Tom about their design work on the CS5 Loudspeakers. One issue, and a large one, how to pull the amount of current from the amplifier to adequately make the bass come alive. 
The speaker had a stated bottom of about 22Hz as I recall. Jim said that they decided that if the impedance dropped enough, that that would pull the amount of current needed to adequately fund the bass. (just as the 3.7 drops in impedance in the lower bass) After the speakers were finished, he and I had dinner and Jim expressed his disappointment in the published specs of the big boy amps versus the reality of their capabilities in producing power into diminishing resistance. It seems that they were not nearly as powerful as claimed.
Back then, Gryphon, now a powerhouse amplifier, was woefully inadequate in playing program material on my CS5's at even moderate levels, with music having deep bass.
As Jim said, 'Every solve creates another challenge', or words to that effect.
So, tmsrdg, I'd check a review or two on your amp, I'm thinking you're right about the congestion issue. Possibly they don't rate their amp into 2 ohms is because it doesn't do well. Many don't.
Best,
Larry

Forgot this. The CS5 dropped to about 2.2ohms if I recall. The design philosophy for bass in the 3.7's was very similar.
Larry

IMF were best speakers I ever heard for Symphonic Music !

tmsrdg, power isn't the most illuminating word, current into low impedance is a subset of power and the operative limitation. You can find out the 2-ohm spec on your amp, which should describe its capability. But, as Larry adds another consideration, current delivery spec can be construed over various time windows, so the spec can lie with demanding program material. Larry is right that Jim was a bit gobsmacked by the subjective experience of CS5 (and all our big products) users running out of bass power. The CS5 came after the CS3.5 with equalized bass, which also drew bass current, but at higher impedance than the CS5. We used a 250W Krell powerhouse which performs as rated, 1000WPC into 2 ohms. Jim assumed the role of the speakers was to perform to its stated specs, and the amp must do likewise and so forth. When manufacturers fudge such claims, the burden-in-fact falls to the speaker for under-performing. All these years later, these matters are still foggy in the mind of the audiophile world. Awhile ago I mentioned that I wish Thiel products had higher impedance minimums - 4ohms minimum as beetlemania (?) corrected my 6 ohm nominal wish. Same animal. We would all be better served via honest claims for our products. 

That series of Classe amps definitely doesn't double into 2 ohms.  I have a pair of the 200s and they were 200/400/500 watts into 8/4/2 ohms.  It's hard for me to imagine 600 watts/side isn't enough.  Much more than that and your amp will be in danger of blowing a fuse.  If you're listening to a full orchestra loud on the 3.7s you may be running up against the limitations of the speakers.  They do fine at a pretty high volume but first order crossovers definitely have volume limitations.