From what I have read in reports of thise who have had a chance to compare the SR-009 with the SR-007 MK1, the fundamental difference between the two is that the SR-009 has vastly superior clarity and that Stax has gone away from the "warmth" avenue and into the "clarity" avenue.
Now this may sound as a surprise to many people, but the SR-007 is not to my ears a warm headphone at all. It is full bodied- but not warm. Now I must admit that it does sound warm using pretty much all the standard sources, amps, and IC's- and therefore it has got the reputation that it is warm- fair enough.
However, on my BHSE, with GE6CA7 tubes and Ridge Street Audio Poemia IC's and very importantly- all fuses in my system are Hi-Fi tuning supreme audiofile fuses- the transparancy is piercing. I have never heard better clarity from any other headphone in my life with the possible exception of those that give up bass response and or have trebble peak. In this set up there is NO WARMTH. There is fullneess, body, and piercing dynamic punch and clarity- like I have never heard before. In fact, sometimes, the clarity is to much for me and I need to switch to a copper IC to warm things up just a tad.
Now I know not everyone can afford or even wants a system like I have. I just want to make the point that when properly driven- and a BHSE is not enough because the tubes and Ridge Street IC's, and the audiophile fuses make a BIG difference- no normal person would claim that the SR-007 is warm.
If the SR-009 is by nature clearer and more transparent than the SR-007- in my set up- I think I may go deaf from to much detail.
Well, glad you brought this up. So maybe a superbly transparent amp (BHSE) & headphone (SR009), can be too revealing? Glad I got a tube output sources!