I had meant to do a full review of the SA6's with a comparison to the E530's as I owned E500/E530's for quite some time and replaced them with SA6's, unfortunately I hit a very busy spell at work and it got put on the backburner.
Yes I replaced my E500's with SA6's but that's not to say the SA6's are clearly better, I'd put them in the same league, they're just somewhat different. As mentioned with Sleek's VQ system the SA6's have the capability to have a more present and extended treble range than the Shure's but it's also possible to knock it back to be more similar to the Shure's if that's your preference. No matter what though, the SA6's have a clean, clear, sibilance free treble which is a must for me.
The biggest differences between the two are probably transient speed and decay rate. The SA6's are faster both in transient speed and decay which IMO gives them a better sense of PRaT. The E500's on the other hand have a somewhat fuller sound that, while a bit slower does tend to capture tonality a little more. A good illustration for the difference might be acoustic guitar, I noted on the E500's one got a better sense of the resonance and tone of the body but the transients of the actual notes being played were softened. The SA6's on the other hand lacked some of the body the E500's had but they handled the transients in a much more realistic fashion.
When the comparing the mids I noticed that the E500's seemed to have a funny rise whereas the SA6's seemed more even and natural sounding.
Bass is another area that can be altered quite a bit with the SA6's and depending on the port along with the combination of treble tubes used the character can change somewhat. Certain combinations just seem to work better for me particularly with respect to PRaT. The SA6's extend down just to the nether regions just as well if not better than the E500's and I believe it's possible for the SA6's to get the bass of the SA6's to a similar volume but again, the E500's sound a bit fuller through the bass whereas the SA6's are snappier which gives one a sense that the E500's have more. Another aspect of the SA6's is they don't have quite the transient snap on drums, this is somewhat dependant on the VQ configuration, in my current configuration it's not really an issue but it is something I've noticed. This is a bit contrary to the overall nature of the SA6's but I suspect it's more correct and the bit of funny push in the E500's midrange I noted may be giving snare drums that little extra pop.
Soundstage is another fairly significant difference. The E500's are the only IEM that I've tried that is able to push the image out so vocals are more in front of you than right in your head. The SA6's don't accomplish this feat, the image starts more in your head and it doesn't have quite the width but they do have better depth going almost as far back as the E500's and the SA6's also have better height than the E500's.
Overall, when it came down to sound it was a bit of a toss up, I really like the full sound of the E500's but the SA6's aren't too far off the mark in this regard and IMO make up for it with their better transient response. Add in the ability to fine tune the sound to preference, replaceable cables, the ability to wear them straight down or over the ear, a much more comfortable fit for me, a cheaper price and the excellent customer service the SA6's were a no-brainer for me.
Edit: I just wrote this up quick so it's a bit rough, hopefully it comes across ok but if not just ask for clarifications and I'll do my best to answer.