My 007k1 pads are brown ones, very stiff (I wonder if they're supposed to be like or the foam deteriorated with age / got stiffer?). So, trying the current 009 pads on it would seem like a good try (009 pads are so much more comfortable).
The change in pads can be as if not even more drastic than the change in diaphragm so you're probably onto something here...
That is my experience too: it's unbelievable how much change different pads can do. Of course the diaphragm is an invariant, and imposes natural limits to the headphones, but pads can change the sound significantly, and eventually change the game for the given headphone.
All the 007 pads I have are quite different. The old-old brown type is made from thicker leather, rather soft. The foam insider got smaller and more soft over time. The sound is round and soft in comparison with the others.
The newer brown 007 Mk1 type is from thinner and finer leather, very soft too, like the best expensive gloves. This is the one I modified, and they are the most comfortable of all. It had somewhat stiffer internal foam, and had a pretty good sound to start with, and with the mods it became rather excellent.
The black Mk2 pads are again from stiffer leather and stiffer foam; they are also thicker, not so comfy as either of the old ones. But these do sound perhaps the best in the stock form, maybe a bit deeper bass, and somewhat more open sound. IIRC Spritzer is using these pads (and Mk2 assembly with Mk1 drivers).
The 009 pads are from higher quality thick leather, and the leather ring securing the headphone is actually reinforced with lining from inside (or it's pleather), making it much more durable to pad changes. This is the best Stax pad design to this date (I only wish they would also experiment with felt, wool and open cell carbon foam instead of using the same closed cell foams for 20-30 years). The leather is not as soft as the newer brown 007 Mk1 pads mainly because the thickness. It may be possible to treat it to become softer, but I agree they are rather comfortable as they are.
The foam inside is rather soft and quite shallow. With the 007 that causes the front of the driver getting a tad too close to the ear, resulting in some midrange elevation. My ears are a few dB's more sensitive to the 1-3 kHz region than the normal (I know everyone is more sensitive to this region, but I do have an anomaly, corrected by my brain and aging to most extent, but still a tendency), so it actually may be fine with most people. For myself, I will experiment with assembling a 2 mm thick felt ring inside the pad on the top of the foam (this is non-destructive) to see if it helps.
The improvement over the stock 007 Mk1 is quite evident, but not as dramatic as with the Fostex TH900, which became a different class of a headphone after the mods (carbon foam ear pad insert, felt ring damper and cup damping). That is one's dream headphone for personal tuning headroom
. Still, the 007 improvements may be a game changer for many people.
Beware that after mounting the 009 pads you need to adjust the head bands as well! Uniform pressure over the ear with slightly-slightly more pressure in the bottom (so need to change the shape), setting it the pressure against the ears not too tight and not too loose either. There is a sweet spot when the sound stage and the tonality is the best. Once you find that spot, will know what to be after and how to set the head bands next time
.
I listened to them this morning too (my morning ears are the best), and it was a fresh experience, pure pleasure, confirming the findings. Anyone having a 007 Mk1 should hear it with the 009 pads (I know it's a big statement, but that's why the invitation to try it out). Then, once you get a taste how big difference pads can make, perhaps you'll feel more inclination to experiment with different materials
. Which I ended up doing during the past year. Now I am nearly done, only hoping I could get the 007 a deep bass with a visceral impact similar of the modded TH900. Once you hear that there is no way back. Though the 009 may have better potential for achieving it via pad mods. Ehh, so pity I can't listen to a 009 in my area easily.