I think until you have spent alot of time with the 900 its hard to judge it as some one dimensional, basshead, "Can for Cretins". Not that I am implying this is what you meant shabta in your post, although the "Beats" reference was cutting it a little close
.
Seriously though, both headphones compliment each other perfectly. For Jazz and Classical (speed / detail / retrieval) the 800 is a great choice for most everything else the 900 excels (although it does it all amazingly good also).
Keep in mind that the 900 is a very complex, sophisticated, and technically proficient headphone that can easily rival all of the other top tier offerings.
Two different flavours of high end headphone goodness.
Another Head-Fier mentioned something about equalizing and that the 800 can be equalized to earth moving bass levels, while this may hold some truth the fact of the matter is that with over eqing the rest of the sound spectrum is lost / suffers.
IMO a headphone is designed a certain way to sound a certain way right out of the box in its virgin form and although we can modify its "God" given sound at the end of the day it is really what the designers created it to be.
Equalizing and modding will only get you so far. The headphones DNA needs to be geared towards a certain sound right from the get go.
My opinions are from someone who appreciates both headphones immensly. Both suffer from a few weaknesses and both excel at what they do well.
Ying and Yang.