For me the HD800 is much better - apart from the fact that I can't wear the Abyss for more than 10 min. w/o getting a headache from the weight. The HD800 has a much better sound stage and the Abyss clearly produces an "inside the head" impression for me. An absolute no go in my book.
At a level of HD800, Abyss, SR-009, LCD-3 it's about personal preference in sound signature and personal music preference and not about the price sticker. The sound of the HD800 and Abyss are pretty different and the SAA will not turn the HD800 into something that sounds like the Abyss ... just a guess , as I haven't had my HD800 modded
So I think you could tell me what amp drives your HD800 as it would help me a lot to make mines sound better.