I feel like all IEMs with connectorized inputs are "balanced-ready". That said, most of them have low enough impedance that a ~1 Vac driving voltage would be more than sufficient. I haven't perceived an audible improvement with my IEMs in TRRS or TRS on the ES100. My HD 6XX, on the other hand, needs that voltage it to get to a usable SPL.
@arbiter76 might be referring to
balanced armature drivers (such as the all-BA ER4 series). Those ARE connectorized, though with a more proprietary keyed system. If the cable fails, though, it can be replaced. Etymotic is also decent about upgrade deals, so there's some measure of loyalty rewards.
At $100-150, it's tough to find a really good all-BA IEM. The FiiO FA1 might be a candidate, but the data hasn't come in yet. There are hybrid options in that price range; the FiiO F9 Pro is an excellent choice, especially when one has the option to apply EQ in the ES100.