Best amp pairing with Aerial Acoustics Speakers?

" .But now with Theta being mostly Class D amps "

Not the Theta Dreadnaugt Mark 1 or 2. Traditional design and you can save a lot of money if you find a good used one. It's a multichannel amp so you would use 4 channels in a vertical biamp. Also, that amp was designed by Ayre, so it makes sense so recommend them as well. In my own system I do a vertical biamp with a pair of V-5's. That would be another good option, and you can start out with just 1 amp.

Whats a "good price"  for a used Dread II?  Would you rate that over Levinson or Simaudio?

Does anyone think that the new ATI Digital Class D amps would be good with the Aerial 7b's?

Jrunr, in looking at the impedance graph measurements in the Stereophile review of your Arial 7B's it seems you are in a similar situation as I am with my Infinity Kappa 9's. Your speakers are not hard to drive on the top end but do present a challenge to drive on the low end. One solution is to horizontally bi-amp them using two different amps speced for their unique loads .

Put your money into the best sounding amp for the top end but buy a more moderately priced amp for the bottom end that can handle the higher current needs. There are many pre-owned amp options to achieve this configuration. I went with a 75 watt tube amp on the top and a high current mid-FI SS amp on the bottom with very very good results. The mid-FI SS amp sounds like crap on the top end but great on the bottom. It is much more expensive to find a single amp solution with high current that can drive the entire speaker with good sonic results. It is the mids and highs that really reveal amp musicality and imperfections so put your money there.

Your speakers, even though rated at 6 Ohms, go down to 3ohms at 400 Hz frequency. Don't make the mistake of thinking high wattage is the same as high current. If you go class D don't get distracted by all the high wattage specs. It seems that Class D is good at generating high watts but if you find a class D amp that also has high current capability under 2 ohms I would like to hear about it.

" Your speakers are not hard to drive on the top end but do present a challenge to drive on the low end. One solution is to horizontally bi-amp them using two different amps speced for their unique loads ."

That sounds like a good idea, but in practice using 2 different amps horizontal is nothing short of a train wreck. The only systems I've seen that type of setup work, was when someone was desperate to fix a problem. And even then, they should have just fixed it the right way.