If you like the bass on the ESL-57 then I'm sure the SR-009 will keep you happy as long as you don't listen at ear bleeding volumes. When I owned the Quad in the 80’s I had to use a MK subwoofer with them, but I don't find the 009 bass to be lacking as long as I don't push them too hard, and it's very fast and textured. I do find that at extreme volumes when I add more volume that the 009 mids and highs get louder more than the bass does, and the balance shifts away from the bass, but my HE-60 do this too.
Still, the 009 bass is actually fuller and more present than the bass on my HE-60 under most listening conditions (but nothing like the O2 mk1). I think the 007 and 009 are both nice to have, by giving me different sound signatures that I can pick from depending on my mood or program material - the 007 being warmer and more laid back, and 009 being more crisp and vivid in the mids. Having the HE-60 seems redundant now, but these two phones complement each other, just like adding an HD800, HE-500 or T1 to my LCD-2 rev1 for non-electrostatic listening.