I am hearing a slightly less treble glare/etch with the grill removed BUT that grill is all important to protect rear from the strong magnetic attraction from there...Sadly, the photos seem to be gone, but most of this discussion traces back to arnaud's measurements in 2010 regarding reflections in the cup: http://www.head-fi.org/t/468461/hd800-imaging-and-treble-why-and-how-it-can-be-improved-upon
Hmm time to try some super thin shelf liner..
edit:
Sorry I just realized this is impressions thread and I know alot members here have been thru their share of cans before or after arriving at the hd800. .
I posted brief impressions/comparisons on all the headphones I owned in my profile if anyone interested in indirect comparisons. .