These (the SR-003) are the same headphone as SR-001mk2 but with the standard plug so it can be used with normal Stax Amps. In the SRS-005 system it comes with the SRM-212 amp. There have been many comparisons of its baby brother, the SR-001mk2, to the Ety ER4 series, so if you do a search you will find the info you are looking for. One person (edstrelow) has compared the SR-001 with its portable amp to the SR-003 with a non-portable amp and found that the differences weren't that great, so the comparisons of the Etys with the SR-001mk2 should give you a pretty good idea of what Ety vs. SRS-005 would be like.
I have the SRS-005 and absolutely love them. I've also heard the Etys briefly (10 minutes) and loved them too. Sorry I can't give you a better comparison than that. The SRS-005 don't isolate very much, perhaps slightly more than a standard earbud. I find them quite comfortable, others may not. I don't find the treble rolled off as has been stated in reviews of SR-001mk2, but I'm not a huge fan of "detailed" treble heavy headphones. However, I love the SR-404 which some people call bright, so go figure.
I will say that I've never heard guitars sound better than on my SRS-005 system, and that like other electrostats it separates the instruments extremely well and never sounds congested in music with gobs of instruments. It may be the fastest headphone out there with such a miniscule moving mass. For me it has what some refer to as the "magic" of electrostats, and at a very attractive price.
Hope this helps!