I did read a little over on headfi and changstar about the mod but I'm bit lost on what materials to buy over here ninja.
do you have any links suggestions on what materials to buy ?
I'm not sure about amps yet mate ....They sound so thin with no weight and I cant see them changing that much... maybe I;m wrong.
Plus I'm only using them on a computer soundcard (creative ZxR) ....some tracks sound amazing though

yes maybe the hd800s is an overkill for my computer

Even upping the bass with eq the bass weight is still missing ....my old hd600 have more weight and slam with my crack amp. I think sennheiser failed a bit with the hd800

I did try the hd700 and t90 in a shop though, they sounded too bright I did love the comfort on the hd700's ...comfort is number 1 when i buy headphones.
yeah my crack amp has the speedball upgrade and mk film caps...and did try a very expensive volume pot. have loads of tubes but still looking for that gec

at a good price! you can spend more money on tubes than the amp itself

but its good fun though
Peace
edit .
I just changed my philips miniwatt tube for a mullard cv491 and the bass is bit better now more fuller sound ..I did try this tube when I first got my hd800s but its sounds way different now
still though these headphones dont make me feel all grovvy like my hd600s do