Tweety,
As a GMA C1.5i owner I can help a little to answer your questions:
In general, the speaker design philosophy @ GMA is to design a speaker that intrudes the very least on the music playing. Roy determined that the best way to do so was to add as little phase shift to the speaker as possible hence he settled on a 1st-order xover circuit. As know, phase & frequency are inextricably linked - if there is a blip in the freq. response, there will be a phase implication & vice-versa. 1st-order xover circuits have a very gentle roll-off hence they intrude the very least into the freq. band of interest thereby they least screw-up the response in the said freq. band. The disadvantage of 1st-order xover circuits is that drivers are not as well protected from each other i.e. some woofer signal leaks into the mid, some mid signal leaks into the tweeter & these type of speakers cannot play as loud as some speakers of the same physical size. However, in all the speakers Roy has designed presently, the phase shift from 300Hz to 8KHz is less than 1 degree! Do some research & look @ specs of many, many other speakers & see what their phase shift is in this freq. range. You will notice that these other speakers' phase shift is all over the map in the 300Hz - 8KHz region. Aside from this, Roy has figured out how his xover circuits can provide a constant impedance to the amplifier using the correct topology Zobel circuits. This makes the speaker a very easy load to drive hence virtually any amplifier can be used & will sound good with his speakers.
Roy also has chosen drivers that are very linear in their resp. freq. ranges of operation. This means that each driver holds its own (i.e. is moving pistonically) before it gets crossed over. Thus, there is minimal distortion from the driver while it is actively reproducing music.
All these aspects (notably minimal phase shift) help to create a speaker that is very true to the recorded music. The timbral accuracy is very high & one always gets a feeling of the performer being in one's room. Thus, customers always feel that the speaker far out does is asking price.
Hope that this helps. FWIW. IMHO.
FYI: I am merely a satisfied customer. I do not represent GMA in any form or fashion. I know what I wrote only because I did extensive research on GMA speakers before buying it. I am also trained as an EE so many concepts of speaker design & acoustics are well within my grasp.