Had considered that, but would like to know if there are any other options. Loved the ER4s but a touch more bass wouldn't go amiss, but only as long as any replacement has equivalent quality to the ER4s....
I am in the UK and the replacement service to here is not cheap($50 shipping)
Get red or orange filters instead of the stock green ones for a little more bass. Search this forum for "etymotic nrb mod" and you'll find the thread with more info on sound and where to buy. It's very cheap.
There is nothing as accurate as the ER4 yet, so I wouldn't spend the extra $$ to try other items when it would be cheaper to just replace your ety.
Etymotic will replace the broken driver for $80. Even with the high shipping, it's still a good deal. Also, changing tips can improve the bass. I use Klipsch tips with mine. Shure olives are also very popular.