For the 111 to match the ER4S so closely in FR with just one single BA from Knowles, it has to be the ED-29689.
The ER4S is difficult to drive because it contains 78 ohms in series attached to the ED driver (for a total of 105 ohm DC resistance = 100 ohm impedance when the reactance of the ED driver is factored in; see picture diagram).
I'd like to find out what the impedance of the TG! 111 is, to see what the effects are of the titanium (or is it stainless steel?) tube are on FR. AFAIK, the ER4 all use 1500 ohm of acoustic resistance on their dampers; it's possible FitEar changed both the dampers and resistance to provide a better match with the metal sound tube, or it could be all the same.
If they do manage to provide an ER4S response in an easy-to-drive package, plus the comfort of an over-ear design, I think the TO GO! 111 will be a hit with recording/mixing/mastering engineers all around. ~$490 is not that much of a premium over the Etymotic asking price given the numerous comfort benefits. I'm sure industry professionals in Japan will be clamoring for it.
Is that diagram from Etymotic because it looks like the BA and 56 ohm resistor are in parallel making the overall impedance of all three positions about 28 ohms, The driver is 7 ohms on it's own. I would think the circuit would look more like this.