I haven't heard any of their BA IEMs, but the ER2SE is fantastic. I haven't measured it, just listened to it. I am using it with the default tri-flange silicone tips, and I find that the bass is more than enough for me. The only thing that could be improved is the treble extension, I feel that depending on the source it lacks a little bit of air, but some people have commented on using the brown filters to open up the treble a little bit, so I am going to try that.
Is there a source for just the brown filters, or do I need to buy Etymotic's tuning kit? If so, it is quite disappointing, as I have no intention of using the red or orange filters at all, which are supposed to make the earphone even darker.
Compared to a great headphone like the HD-540 II, I feel the ER2SE has slighly less extension on the bass and somewhat less extension in the treble, plus the soundstage is like a night and day difference. The tonal balance is excellent, and details are good. I got this for $50 from Adorama last year, so it is probably the best audio buy ever for me.