1. It's so called Luxury Edition limited to 26 pairs of Trio G2 series before the introduction of Trio G3 owned by Todd (
@sbnx) .The main differences to the regular G2 Trios are : more rigid frame, better capacitors and internal cabling ( gold/silver afaik).
You can find more info on Soundrebels website, it's in polish but I hope you will find easily the way to translate it with google.
Avantgarde Acoustic Trio Luxury Edition 26 – Soundrebels
2. Yes, I have purchased only Trio towers without any Avantgarde subs. The small 231 subs ( used during soundrebels test ) are imho suboptimal for Trios and I did not have space in my place to install basshorns . So I decided to try the third party subs and finished with 4 REL Carbon Special. I shared my thoughts here :
Avantgarde Horn Speakers | What's Best Audio and Video Forum. The Best High End Audio Forum on the planet! (whatsbestforum.com)
3. One of the main reasons I decide to buy REL Carbon Special subs is that they reproduce the bass up to 120 Hz and match perfectly the natural roll-of of the big horn which is - according to the technical specification - at 100 Hz, but according to many opinions it's more like 110-120 Hz.
The downside of REL subs is that there is no DSP available so I had to tune them by ear , the advantge is that the bass quality of carbon membranes is much better than this from 231 AG subs. They are also very well finished in piano black which is important in our living room because my setup is placed next to the piano. For sure the AG basshorns remain the best solution but I am quite happy with the sound I have despite the fact that this is a kind of compromise.