I have the SR-001. It's the same as the 003 except that it comes with its own energiser which it can only work with due to its dedicated plug for that energiser. The 003 has the standard Stax plug so it can work with any Stax energiser.
As for sound quality, first and foremost, and most important of all - its extremely musical. Much more so than the Ety ER4P and Shure SE530 that I also own. It sounds quite effortless, another of its appealing qualities. Other than that, its bass in a bit laid back (not prominent) but it actually goes quite deep, more so than the SE530. Of the three, this is certainly my fav. However after recently getting the FAD 1601SB, I have to say that the FAD's trounce the SR-001 in every way; but then the FAD's are almost three times the price too.
I last compared the 003 against the Omega and Lambda almost three years back, but what I remember is that naturally both those bigger phones were more authoritative and had deeper more powerful bass. However the family sound was certainly there amongst all three and the 003 acquitted itself rather well.
Lastly, bear in mind that the 001/003 don't isolate at all.