I've only had them since this morning. But so far I'm really digging the sound
Some initial impressions. Very balanced sound with exceptional tonality. The first thing I noticed is how forward the sound signature is (similar to the K1000). The soundstage isn't as large as the Omega 2 MK1. The Omega 2 has this uncanny ability to throw its voice like a ventriloquist projecting sounds outside the dimensions of the earspeaker. The Koss can't quite do that.
The Koss have very, very nice midbass and impact making them fun to listen to with rock. They have a hint of that deep bass that is crying to come out, but doesn't extend that far.
Mids and highs are very well balanced and nicely detailed. I still prefer the mids on the Omega 2, they have the ability to completely disappear.
Just to see how they scale with the stock amp I swapped out the North Star M192 with my Denon DA-500 and then an old Panasonic DVD player. The ESP scale very nicely.
Detail and imaging will take a bit longer to nail down, I'll need to listen to more reference recordings. They still possess that effortless nature of electrostats, like there isn't any hint of them struggling to keep up (sort of hard to describe in words )
Non sound impressions:
Build quality isn't so great. They feel a bit flimsy. The stock cable must be like 3-3.5 feet, were they expecting us to use a shirt pocket amp without the extension cable
Comfort is above average. Again I prefer the Omega 2. The Koss are similar to the Lambdas as far as comfort goes.