Moseboy, I used to own the SE530 and while I enjoyed its midrange for a while, I came to see that it was artificially boosted at the expense of the rest of the frequency spectrum. If you really value midrange richness, then I think you're looking in the right place with the ES5. It's much more balanced in relation to the bass and treble, and instrument separation and soundstage are far better IMO. If you want even more forwardness, it seems the ES3x may be worth looking into as well (but it may not have the refinements that Westone has made with the ES5).
You don't have to worry about losing any bass quality, because the ES5 has very textured and focused bass. In terms of pure quantity, I'm not sure, but I remember the SE530 having a slight midbass bloat so that wouldn't be desirable to me. And the ES5 won't distort at high (listenable) volumes--this is a finely crafted piece of equipment. Then again, I haven't heard any headphones' bass distorting at high volumes except for crappy iBuds. I guess I never cranked it up that high with the SE530, but I'd be surprised if it distorted, but maybe it got slightly flabby and uncontrolled.