Ciro...Andy Payor of Rockport is very approachable and happy to talk about his designs, so giving him a call will yield the best answer to your question. I have heard the Miras, the Ankaa's and the Aquila's but not the Altairs. I think Branislav's answer is a very good one. There is a house sound to Rockport speakers that is shared across the speaker line. What you get with each step up in the line, is greater extension at the frequency extremes, more constrained damping in the enclosures for reduced impact of cabinet resonances, resulting in a more resolving sound, and greater ability to move air for larger listening rooms.
What is the house sound? My impression of it is as follows: Rockport speakers' midrange is beguiling. The bass is textured and full, yet still punchy and articulate. The treble is smooth and grain free but not spotlit or in your face. Also, I would say the Rockports image well and throw a wide and deep soundstage but they can be bettered in these arenas by more "hifi" speakers. Finally where the Rockports clinch it for me is the dynamic range of the speakers and their propulsive quality. They present a more exciting and rythmically engaging sound for me.
