After a couple of years since it came out, I have finally laid my hands on a SR-009, and had a chance to compare it thoroughly to two SR-007 (Omega 2), as well as a SR-003 (“Babystax”). The SR-007’s we have in our circle of friends are very different: one is the ‘dark’ type, which I consider to be the worst; the other is the ‘bright’ type, which is far better than the dark one.
Initially, I was hoping that the SR-009 would fall short of the best Omega 2, since the SR-009 is far more expensive.
The truth is that the SR-009 are superior, and it’s something really special.

The SR-009 basically have all the good qualities of the best Stax, blended together. There is a sense of energy, envelopment, fullness , midrange richness that the 007 don’t have.
The 009 are not bright either: they are darker/fuller than the “good” sr007, which lacks color by comparison.
The SR-009  only lose to the SR-007 in one aspect: soundstaging.
Like Head-di’er spritzer once said, the 009 are always wide. The “better” SR-007 have a more layered soundstage, which is generally narrower, but is capable of bigger projections of instruments, passing from a small to a big “bubble” of music. With the 009, the soundstage is more constantly wide.
Everything else is better (or on par) with the 009: detail is exceptional with both the SR-009 and the ‘bright’ SR-007. It’s presented differently, because the SR-009 offer more separation in a wider space, while the SR-007 keep all the sounds more focused to the center.
 

 
We made our comparisons using the AMR DP-777 DAC, and two electrostatic amplifiers: the Headamp KGSS and the Stax SRM-007t.
The SR-009 is much better than the SR-007 in both cases. The KGSS + 009 turned out as the best combo. Anyway, even with the SRM-007t, the SR-009 is still noticeably better than the SR-007 with the KGSS (the 007t/007 combo being the worst of the lot).
The SR-009 wins thanks to its realistic and lively presentation; with the 007t, the bass only gets flabbier.

In a subsequent session, we compared the SR-003 and the SR-009 using only the SRM-007t (and the DP-777 DAC).
The 003 are amazing, as they are the closest Stax to the 009 tonally.
In the past, there was a sort of myth: that the SR-003 were similar to the SR-007, given they both have a round driver. We dispelled such myth long ago, since the two Stax headphones have noticeably different tonal balance. It was simply wishful thinking, for the people of us who were hoping to stop at the cheaper Stax headphone.
Anyway, comparing the SR-003 and the SR-009, we discovered that the 009 are the real ‘grown up’ 003, offering a similar midrange concentration, warmth and solidity. The 009 have much wider soundstage, offer higher separation and have much more extended and powerful bass, but there is a striking overall similarity in tonal intensity and immediacy. We could say that from the 003 to the 009 there is only one real big stop (if one doesnt want any compromises).
Any other Stax in the middle (including the SR-007, because of its midrange paleness) offers compromises compared to the SR-003 and its magical presentation and lush midrange-to-treble balance.
 

 
We also tried a pair of Koss ESP950 and compared it directly to the SR-009. The difference is huge: the Koss have a sort of “vintage” sound, they are midrangey and light sounding compared to both the 007 and 009. I was pretty intrigued by this real life difference, since, once, I had a chance to look at the frequency response graphics for the ESP950 and the SR-009 on Inner Fidelity, and they were looking very similar. But they are really nothing alike.

I came away desiring to buy a SR-009 for myself, finding it the first total “no compromise” headphone I have personally heard.

As I have written elsewhere: “You put a great, analogue sounding source with the SR-009 and the sound is magical. You put a great, analogue sounding source behind the SR-007, and someone will tell you that your amp is the problem, and/or your source is not enough”.