The he60 is the affordable version of the Orpheus, often referred to as the 'Baby Orpheus'. This is mainly due to the lack of a real amp, and the (supposedly) lesser quality as compared to it's sibling the HE90/HEV90, which sells for >$20k, based on recent sales.
 
Personally, I think there are better amps than the hev90 (eXStatA, Blue Hawaii), but ANY electrostatic amp is better than the hev70 - literally.
 
So, let's focus on the he60. When driven by a capable amp (which excludes the hev70, and almost all Stax amps), this phone is unparalleled in detail and speed. Often, electrostats are noted to be bass shy, but not the he60, and it's closest rival, the Stax Omega II. In the electrostatic world, there are few choices, and fewer still flavors. Those who tend to like the OII are generally not as fond of the he60/he90, and vice versa. Personally, I find the OII too dark, hard to fit, and generally not at all to my taste, where as the he60/he90 is more voiced for my listening preferences.
 
The he60 can scale up to any amp and source thrown at it, and is relatively affordable when available, which cannot be said of the he90. One mod that is de rigeur would be reterminating to a Stax 5pin (pro bias) plug, as the hev70 connection is in no way compatible with any other connection.
 
Regarding amps, my personal favorites have been the KGBH and the eXStatA, where the KGSS, Woo GES, and anything manufactured by Stax (252, SRM T1, 727, 717, etc) I simply found lacking. Some of this may well have been that all standard Stax bias is 580v, where the he60 is 540v, but hybrids are definitely my strong favorite ofer SS, wrt electrostats. There is a warmth added to the clinical tendancies of stats that add just a touch of flavor, but not coloration.
 
In a nutshell, these are out of production, some parts are no longer available (earcushions for one), and appeal to a subjective preference in tone. If you are a Senn fan, you will note the signature from it's cousins, the hd600/650/800, and yet, note this can reproduce signal like they just can't. That said, they simply cannot transfer bone jarring bass like the hd800, and require a dedicated electrostatic amp.
 
If precision is the game, the he60 is a player. Electrostats are different, and you better be prepared to invest in the chain that goes with them, otherwise, temper your expectations.

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.