In general, OTL's like high impedance loudspeakers of fairly high efficiency. Eight ohms is usually okay, but many "8 ohm" speakers dip well below 8 ohms in the upper bass or at crossover frequencies.
Also, since OTL's have a high output impedance, they aren't as good at controlling the bottom end if the woofer has a high Qms. On the other hand, low Qms woofers don't rely on the amplifier as much for controlling the woofer's motion, so they work better with OTL amps. Unfortunately, this information is seldom published by loudspeaker system manufacturers.
PHY full-range drivers work very well with OTL amps, as do most full-range drivers (the honest 8-ohm Omega line comes do mind, as does the Cain & Cain line and Lowther-based systems). The Classic Audio Reproductions T-5 works quite well with even the smallest Atma-Sphere OTL amps, and I would expect the high impedance Coincidents to work very well also. Among electrostats, it's true that a powerful (100 watt or more) OTL amp will drive the big Sound Labs, but with a less powerful OTL amp the Quads (ideally the original ESL's - the "57's") would probably be a better match. Disclaimer - I'm a PHY and Omega and Sound Lab dealer.
Best of luck in your quest!
Duke
