FWIW, I had the 4.A (which I sold about a month or so ago).. going off memory, the AS-2 demo/prototype/whatever I heard (in July of 2012) smoked it. I've forgotten some of the nuances of the AS-2, but it was impressive enough that it made lasting impression on me. Both phones favor a largely neutral signature.. but the AS-2 prototype/demo's technicalities were far more impressive to me. The 4.A was a custom fit & the AS-2 was a generic custom, too.. so the AS-2 actually was at a disadvantage in terms of fitment.
Dale's mentioned the AS/G-2 now features a new, built-from-scratch dynamic driver, too. Personally speaking, I'd be more than confident using my experience to conclude the ASG-2 will be a better performing monitor than the 4.Ai (personal sound preferences aside, of course).
The build on my 4.A was sublime, though. Heir's artistic capabilities are second to none.