SETs whose power outputs are in the low single digits pretty much require that you match them with high-sensitivity speakers like horns. The range of speakers that the ATM-211 can drive is not nearly as restricted. I did a brief trial with a pair of Paradigm Reference Studio/20 v.2s, which I still had around as part of the associated equipment for a review in Stereophile Guide to Home Theater. The Studio/20's claimed "in-room" sensitivity is 89dB (86dB anechoic), which is more than 10dB lower than that of the Avantgarde Uno. The normal recommended power for a speaker of this sensitivity would be 50W or higher, but, at least in my 16' by 14' by 7.5' listening room, the ATM-211 had no trouble driving the Studio/20s to very satisfactory levels. (As expected, the noise level with the Studio/20s was much lower than with the Unos.)

The question of how much power is enough to drive a given speaker can't be answered without knowing not only how the amp and the speaker interact, but also the size of the room and—most important—the person's listening preferences. I would be reluctant to endorse the ATM-211 as being suitable for all speakers at or above the Studio/20's 89dB/86dB sensitivity, but I would urge that anyone attracted to this amp consider it, even if their speakers are not in the high-sensitivity category.

Conclusions
By my standards—and, I suspect, the standards of most Stereophile readers—$9800 is a lot of money to consider spending on a pair of amplifiers, especially if their output is only 22Wpc. Very good-sounding amplifiers are available for a lot less, the similarly powered $1595 Quicksilver Horn Mono providing a superb value-for-money example. For me, any amplifier that costs nearly $10k must deliver sonic performance that goes significantly beyond that available from other, more sensibly priced alternatives.

The Air Tight ATM-211 does that. Beautifully built, the ATM-211 has a touch of the exotic in its appearance, and offers outstanding transparency, tonal neutrality, soundstage width and depth, and dynamics that make it sound like a much more powerful amplifier. Although the noise level with the ultrasensitive Avantgarde Unos was higher than I would have liked, and I didn't think that the ATM-211 quite matched the midrange magic of low-powered SETs, I felt that, overall, the ATM-211 was probably the best-sounding amplifier I've had in my system.

Footnote 1: Some Stereophile readers have expressed disappointment that reviews do not always make direct comparisons between the component being reviewed and previously reviewed competing products. I agree that comparisons are important, but the logistics of reviewing are such that the ideal A/B comparison is seldom practicable. When the listening part of a review is finished, the product is normally sent to Stereophile to be measured and photographed, and then returned to the manufacturer. Manufacturers typically have only one or two units designated as review samples, and these are sent around to various magazines.—Robert Deutsch