FWIW, SA6's warm and coloured midrange sounds nothing like ER-4. Triple.fi 10 is more neutral, but the treble doesn't sound like ER-4, with the former sounds more like sizzle and the later gives a some what airy feel, but the UE have wider sound stage and better layering. Both has more bottom end than ER-4.
AFAIK there is nothing like the ER-4. If you want a custom you should make a custom mold with it. If you want more bass but not a bass head I suggest you look into the amplification, some amps inherently have a mid bass hump that works well with Etys, which is what I did. I listen to mainly jazz, vocal and acoustic stuffs.
My prototyped 3 drivers IEM model from certain company in Thailand sounds similar to ER-4 (With my crossover preferences, I mean adjusting space, filter type and own 3-way crossover circuit design). However, no ER-4 driver in this model but I really love it though it doesn't have much bass like SE530 but suffice for audiophile bass.
The ACS custom line offer the same drivers as the Ety's. And dont let the lack of ACS ownership on headfi put you off. Andy's probably been around longer than all of the manufacturer's mentioned in this thread. He's helped train the folks at Etymotic and sensaphonics so he knows a thing or two about IEM. And everyone I know who has heard both the UE11 and the ACS IEM have always preffered the latter
I have a pair of etys and I used to think, "wow, such clear and sharp sound!" Then I bought a pair of UE10's and was totally blown away. The improvement over the etys is dramatic - and, yes worth the $$. Sounds like the UE11's are even better, so if you have the cash, that's the way I'd go.
I don't have much experience with the UE's, but the Shure SE530's were a decent improvement over the Ety ER4P. Well, decent in that they had more bass, but the clarity/treble of the Ety's were still better.
Have you tried setting up an EQ for your source? I know it's not the most ideal way about adding bass, but I find the Ety + bass boost EQ to come very close to the Shure SE530.