Thanks James, nice review for Christmas reading!
I briefly tried the IE800 a few days ago, and it came to my surprise as how much bass they have. I can't really remember much of the sound of the IE8, but these things have monstrous bass! The big improvement I feel is the IE800 has more presence in the low-bass, which IMO make the overall bass of the IE800 sound incredibly fun! But then, I found that they have too much mid-bass and upper-bass for me.
They also gave me an impression that the sound is slightly V-shaped. The mids isn't laid back or recessed, but I found the bass and treble are too prominent, that they tend to take away my attention from the mid-range. Tonally, I didn't see any major flaws, they are quite neutral in mid-range to me. I also think the treb though have good extension and detail, it sounds a bit thin, and I thought it could have been more refined.
The details overall isn't the best I have heard from IEM, but they are still better than most of dynamic-based IEM from my experience. The soundstage is about average, but they have good imaging and sound very airy to me (which I like). At the end of the day, what left me impressed about the IE800 are the bass and treble extension, there is no deny that I found they are very fun to listen to. However, as a whole, when considering the price, it is such a let down.
I sure didn't spend enough time with them to give out conclusion, and especially since I only tried them with 1 DAP (my Zune HD), but still, I hope Sennheiser could have done better with the IE800, and I'm sure they could.
A friend of mine, who also tried them, has pretty much the same opinion. His source is iTouch + iQube v2, he said the IE800 sound way too bassy with the iQube, and he prefers the iTouch with no amp.