Well, the AS-2 custom fit are pretty different than the universal fit ie800. Dale Lott has said on hf that he's re-tuning the treble and changing the bass with a new vent in the future, so comparisons can only be with how the AS-2 I have sounds.
I'd say the AS-2 (non-acrylic shell) is the lightest custom I've ever tried. The cable is replaceable and you can wear it comfortably with no microphonics on the stock cable (or replacement cables I've used from Toxic Cables, for that matter). The ie800 is unusable if you're 6 feet tall or over because you'll have trouble wearing it over-ear, which due to the massive microphonics is the only way to go. The AS-2 or universal fit ASG-2 is a better value and some will like the tuning better, although the ie800 is amazing in terms of the sound a single 7mm micro dynamic can produce.
The AS-2 for now has more mid-bass than sub-bass, a warm, thick sound, lifted vocal range and with a treble that's been adjusted to stage use so it's non-fatiguing. The ie800, after only a few days listening and I'm sure my take on it will change, has way more sub-bass, less midbass, a clear midrange and vocal range that lacks edginess and warmth. People are calling it "dry", which might be a good description. I am used to stage monitors that bump the vocal range and add liveliness, but so far I don't hear it as having a deadened sound. The treble was as people described it the first time I put it in my ears (people described it as non-sibilant but having a tizzy, thin quality--it sounded like a twfk armature to me), but the next day, perhaps due to getting a better fit or the non-woven filter, I found it was no longer a problem. The issue was lessened to the point where it didn't distract (I also let them burn in at 110db or so for a few nights). Actually, I tried without the filter now and things are okay. It's definitely a tuning with a certain character, but one that might be very attractive to many people. I've noticed, maybe you have, that although several people have ended up selling or not liking their ie800 on head-fi, they tend to say that when they let their non-hf friends listen to their top iems, the ie800 is usually the favorite! There's something to that. The ie800 is more technically capable and if you can wear it over-ear, it sounds as good or better than anything in-ear custom or universal that I've heard (at least, in my honeymoon phase! Maybe later it'll be different).