Pros: Best dynamic available
Cons: VERY picky about the amp and cable
Let's start with my long love for all things Senn, from my first hd545, to hd600, not so much the hd650, but back again with the he60 (electrostat) and now the hd800.
The search for amps started with a balanced Bijou, where I thought a tube amp would be just the ticket with a SS source (Cambridge 840c), but, not quite. I also tried them balanced with a Little Dot Mark IV... just wasn't quite there.
Keeping with a SS source, I then looked at push-pull amps, where the jury is out, mainly by not having the amp fully functional for a long enough time.
So, I completely switched gears, through an odd congruence of events. First, I upgraded my source significantly, and changed topology to tube from SS. This, combined with a bjt SS amp (a commercial prototype) has given me the answer. With this combination, the hd800 is on par with the he60 (driven with eXStatA, that has better synergy with the he60 than does the BH), but with FAR better bass. Not that the he60, properly driven, is at all bass shy, but the hd800 really makes bass happen. True bass heads will now actually seek out the hd800 with an amp such as this (or KG's dynafet) because this is bass you feel, not just hear.
In fact, I (as a life long bass player) assert the hd800 has BETTER bass (quality and quantity) than the L3000, with FAR better control. Want to hear the timbre of a Fender Precision, or the sharpness of a Jazz, then contrast with an Alembic? This is the headphone for you.
Midrange is the patented Senn sound - nothing better for guitar and piano.
Now, where the discussion will be the most intense is around the higher frequencies - my bias is far away from that region, almost to the enxtent of dismissing it entirely, so I'll leave that for others.
PRaT is dead on, whether it's DEVO, Radiohead, Rhianna, or AC/DC. For the longest while I thought I'd have to get some HE-5 (or whatever the latest flavor) to really make headphones boogie again. Nope, the hd800 is up to the task, with the right supporting cast.
This will be available for listen at CanJam. See for yourself.
No mods per se, but I do have an APS v3 cable, balanced.
The strongest possible recommendation I can give the hd800 is that it would make me find the he60 idle and extraneous, and, I am ALMOST there.