I recently bought a Stax SR-007 Mk1 from macrog, one of the good sounding pieces.
With many kinds of music, I still prefer the 507:
- it has has bigger, wider, taller, albeit more diffuse sound stage than the 007 Mk1
- seems to go deeper, with better deep bass slam
- is much more open and more neutral sounding, in fact sounds almost identical with the best pieces of Senn HD-800 I heard, with more warmth and smoothness.
With classical and instrumental/jazz, the 007 Mk1
- sounds more true to the instrument timbres, although a bit dark
- sounds more shut in, but not veiled and not lacking in treble at all
- better tracking of dynamic gradations in music, transients, inflexions
- better microdynamics
- more midbass slam than the 507 (which has a better deep bass slam)
- much more narrow, but better focused sound stage.
I have heard the SR-007 Mk2 and the SR-009 too. I clearly liked the 507 more than the SR-007 Mk2, and as said, often preferred it over the Mk1 too.
The SR-009 improves the sound in the same direction as the 507 (open, big soundstage etc), but it is far, far better:
- the sound stage is bigger, but also better focused; I like more the 009 imaging than that of the HD800
- has a class better/more musical bass than any other headphone I heard, including the HD800, LCD-3, TH900 (I said better
- every tone is just more true to the real timbre of instruments, too
- sounds smoother, even though the treble has some extra hash; some would say it "adds air around the instruments"
, I would say this could be very slightly improved, but it does not distract anything from enjoying the presentation and does not smear the music
- very good micro- and macro-dynamic gradation, close to perfect transients.
In terms of sound quality, the SR-009 is the headphone to keep for long term, by a big margin. I just hope new developments in materials and electrostatic technology will make this more accessible in the future (check for instance www.piosound.com ), as well as even better. Until then, the 507 is the best price-performance headphone for me. It can be fairly much improved by cryogenic treatment, so I may check the Airbow SC-21 some day, may be worth the price difference. Or, could try a local cryogenic treatment for a start?