Nice! The Concero HP and UERM play very, very nicely together. The HP's great sub-bas articulation really makes up for the roll-off characteristics of the UERM (which, BTW, is sort of an "intentional flaw" in that the UERM is tuned to replicate the sound of a studio near-field monitor like the Yamaha NS10, which would have the same kind of roll-off as well --- it was designed for Capitol personnel to mix on the go and still have the same kind of studio feel, so whatever "flaws" are in their mixing system, they're in the UERM as well, unfortunately). The two together take the word "resolution" to a whole new level, without sacrificing dynamics. The lower-end Resonessence Herus is actually a pretty good combination with the UERM as well, but the UERM picks up hiss with the Herus (tried it via iPad & CCK), as opposed to being dead silent with the HP (regardless of source). People are saying really great things about the Leckerton UHA760 w/AD4627-1B ARZ being super silent and low-gain friendly, but I've never heard any of the Leckertons myself.
The JH13FP is definitely the "technically superior" IEM, but it has an aggressive tuning that, to me, makes me not want to listen to them for more than a single song at a time. The UERM, on the other hand, is decidedly more laid-back in presentation, so it would stay in my ears much longer. I'd actually guess that the Roxanne has less aggressive treble than the JH13FP, which would mean that if they introduced a simpler variant of the Roxanne (whatever she'd be named) without that silly bass knob and a JH13-like signature, it'd probably be better than the current JH13FP.
I hope the Geek Out will be a good pairing as well --- my intention is to hook it up to the Sony NWZ-F886 with
this cable, to make it a super low-profile rig. I'm only afraid that the battery will run out too quickly on the F886, or if it won't be able to provide enough current to the Geek Out, which is why I'm considering the yet-to-be-kickstarted Geek Out Mini, which is supposed to either draw much less current (lower power delivery, single output, and no crossfeed) to be iDevice-compatible (<200 mA) like the Herus, and might actually have a variant that includes its own battery source. I'd happily trade out the Geek Out for one of these "Mini" models if they really do include these features.