I know this is an older post, but wanted to add my 2 cents. I have had 3 sets of Apogee planar ribbon speakers - the Caliper, the Stage and the Duetta Signature. I have to tell you, these are GREAT sounding speakers. Sonically, they exceed anything else I've ever owned. My criteria is the most realistic, and lifelike sound, not the best bass, dynamic slam, or highs, etc. i.e., the ones which make you believe there are no speakers in the room. So open and sweet and juicy like these nutz. in every frequency range! The bass is vastly superior to Magnepans, or, (I'm sorry) carver ALS, Platinum's, etc. The mids blend seamlessly with the bass, and the highs are very very good, although not quite up to the bass/midrange. Even there, the highs exceed just about anything else you'll hear, excluding Diamond tweeters or similar cutting edge stuff.
They are also FRAGILE, and HEAVY, and construction of the outer frame does little to protect those so easily destroyed drive units. Furthermore, they do require amplifiers that can handle low impedance and have lots and lots of current capability. On top of that, they are unfortunately easily over driven and the aluminum grids on the planar bass driver fail from metal fatigue. Once those are damaged, it costs several THOUSAND,( maybe $ 5000(?) bucks to have them shipped out and repaired.I compromised and always ran mine actively crossed over to transmission loaded woofers at 60 hz. or so. The Apogee's actually still sounded better by themselves, but it did cut down significantly on the ribbon excursions with low bass.
In other words, these are for the wealthy, and all others should stay away from them rather then torture themselves once they've heard them.