Thiel Owners

Prof - your information is correct. As a company we aimed our products at living-room listeners. Thus the relatively high cost of our enclosures. We assumed grilles would be in place for listening. Over the years, our fabrics became more sheer and less audible, culminating in perforated metal grilles, which are very transparent.
To various degrees, fabric reduces amplitude in the 1.5 to 8kHz range by as much as 1dB. That’s pretty huge, considering that sophisticated listeners can register 1/10th dB differences when sustained over a broad sonic range. The bare speaker will sound more aggressive, especially in less-treated rooms.
To another point. Thiel’s grille frames were used as a significant mitigation to cabinet edge diffraction, and sometimes as wave guides to shape off-axis dispersion. In the case of a very dead room and a listener preference for the additional brightness content, we highly encourage taking the fabric off the frame and using the frame for its engineered purposes. I have also noted wave propagation effects directly on the baffle surface which are tamed by the fabric itself (on models with fabric touching baffle.) Generally speaking the grille is a significant engineering element and removing it undoes significant design effort. I’ll add that many of the long-standing criticisms of the Thiel sound (up-front, in-your-face, tizzy, harsh, etc.), directly result from removing the grille.

Let’s side-step to your model 02s. That model preceded our knowledge and attention to most of these diffraction and wave-guide considerations, but the frequency response is more accurate with grilles on (and overall performance is probably a toss-up. The Renaissance 02 reworks the grille for considerably higher performance while retaining the general aesthetic of the original 1976 design.

Thoft - to augment unsound’s point - an aspect to consider is voltage sensitivity of a speaker in a room. I like that you can listen at 3/4 volume setting. Many preamp designs lose performance as the volume setting decreases. Often the criticism that a speaker doesn’t perform well at low volume is less a characteristic of the speaker than it is of the amplification driving it. Of course our ears roll off in the bass and treble at lower volume, so speakers with a bloated bass will sound "better" at lower volume. But the preamp considerations are a significant determinant factor. PS Audio’s ’Gain Cell’ solution side-steps the issue and sound "the same" at any volume setting. Such a puzzle. Nice solution. PS's moderately priced Gain Cell DAC-Pre is my go-to preamp for this reason among others.

Thanks very much for the info Tom.  That's what I figured.  I don't have
much urge to take the grills off my 2.7s.

I do find my Joseph speakers benefit somewhat with grills off in terms of opening up the high end and delivering all they are capable of.  At the same time, though, they are actually a bit more coherent with the grills on (high frequencies more seamlessly integrated).   In fact I find many speakers sound a bit more coherent in the top frequencies with the grills on.

Prof - I suppose an 'ultimate' solution would have nothing in front of the drivers, except possibly a phase plug at the apex of the tweeter. The bare baffle then needs propagation control. We used splatter paint and fabric on baffle (in my time) to break up glare. Later, the perf metal may have performed that function. I like my new Ultrasuede on Felt solution. 

Once a designer decides to protect or otherwise hide the drivers, then it's a dance of interacting variables. The user might choose differently than the designer, but often lacks knowledge of the trade-offs. 

Jon_5912,

Back to amp question, you might want to check out Starke Sound's AD4.320. They are on sale, satisfy many of your requirements, offer hassle free 30 day in home trial. A unique D class module boosted to 600kHz and analog power supply. No association other than keen interest. Mine arrived last night but remains boxed.