http://www.innerfidelity.com/images/ShureSE846BlueFilterSample2.pdf look at the "electrical impedance and phase" graph, the impedance is the pink trace.
about the same measure from goldenears, impedance is the lower curve and the impedance value on the left:
so except the rise in the treble that is stiffer on one measure than the other(from my own messing around, it's hard to get anything reliable and changing the value of the resistor used for the measurement can impact this, so maybe they actually are showing an IEM with the same specs).
anyway given the signature of the 846, a little more boost past 15khz isn't going to matter much, so what's important IMO is the curve going down from bass to 5khz.
for people not too confident with electricity, you can still get an idea of what is happening by imagining that the curve is the shape of your EQ. if you use a close to zero ohm impedance source, the EQ would be flat, if you use a source of several ohms, then imagine you're applying and EQ with the shape of the impedance curve. and of course with slightly lower impedance you would get something in between flat and that curve.
edit: some times back I had posted this to try and illustrate what could happen to the 846's signature when changing the impedance, it's not precise(any slight error in the reading of impedance values lead to some massive changes, but the direction and magnitude should not be too far off. you can get an idea of what I said with the impedance curve as EQ trick: http://www.head-fi.org/t/663180/shure-se846-a-new-in-ear-flagship-from-shure-finally-impressions-p26-28/3105#post_11468047
this trick doesn't tell you how much db you will gain or lose at different frequencies(you need ohm's law for that), but it does give you the shape and general direction of the change. here adding impedance(several ohm instead of 0.5ohm) will make the shure to sound warmer.
now what was the IEM using as a source when the guys engineered it? you could go asking this for all IEMs and go mad from not getting much answers ^_^. just know that between impedance and filters you have a pretty wild range of signatures you could use.
the little problem I can see is that most consumer sources are made to be ok driving loads(headphones/IEMs) from the usual 16-300ohm. this IEM goes as low as 5ohm! so it's likely that a few devices will perform less than ideally with the shure plugged into them. sadly I have no magic answer about that, we would need to measure the DAP with such a low load to know (or listen and find something isn't right is the problem is massive). and nobody goes measuring DAPs or amps with a 5ohm load on the web as far as I know.
last time I saw something on the subject it was http://www.jensign.com/S4Distortion/ where the cellphone distorted into low impedance at low volume levels even though it was a lower impedance output than usual(luckily the problem has been fixed).
but I doubt it's an isolated problem with super low impedance IEMs. to some sources, 5ohm starts to look like a short circuit and all the energy now has to be dissipated by the amp itself.
IMO any manufacturer of portable gears should give specs into 8ohm nowadays instead of sticking to 16 or 32ohm as if no IEM ever went below those numbers. but that's just me day dreaming that manufacturers would do the obvious things. ^_^
anyway, adding a few ohm to a troubled source (with resistors in the cable for example) will make the shure warmer, that is a fact, but it might also make the source's life easier as it would now have to drive the shure+the added resistor. so it all depends on the source, for one that works fine it's IMO messing up the shure's signature making it too warm(but that's a matter of taste). for sources that you feel sound better when you use a higher impedance IEM, maybe try to get a resistor adapter or some old school volume attenuator(but that might have greater channel imbalance) and then maybe EQ to go back to something closer to the signature you prefer?
hard to just guess stuff without measurements. most of the time only crosstalk becomes real poor when the IEM is low impedance(and we don't notice unless it's like -30db or something really really poor), the rest doesn't necessarily worsen in a meaningful/audible way.
I hope I'm not confusing people even more, I'm good at not being clear.