Maybe this can make it a bit simpler, though it is most likely posted in a wiki sticky or the sound science section already in some form or another.
It's basically an interaction between player output ohms and the ohms on the cans/iems.
Some things can swing all over the place during use, whereas some are seen as a constant resistive load and not as affected meaning they don't electrically swing around/fluctuate in response/change as much during input signals.( orthodynamics ) and aren't too concerned
Ideally, you should aim for player with an output ohms as low as possible which will accommodate the widest range of cans especially if using low ohm IEM's. Headphones that are at least 8 times ( was that it I forget now )
or more the output of the player
I can't believe they actually released a player with 22 on the output, just limiting ideal can choices though probably fine with fullsized stuff with 250 ohms and upwards but lesser things would get all goofy with being able to adequately deal with the cans impedance ( ohms ) and that's where things get wonky by messing up the electrical aspects of the supply. Throws the headphones "ideal" comfort zone off it was designed towards. I guess like compressing a can of slippery sardines, when it is wider they fit nicely, but when it gets compressed and more cramped ( the range between player and cans ) then things start slipping out of the top, and some pop out completely
.I may be full of crap no expert here.
At least if this simplifies it in BASIC terms GENERALLY it's what i wanted to do.
aw heck i will post this anyhow and regret it later. Not had enough coffee yet for logical thinking. that's what the edit function is for haha
Please fell free to correct the hell out of this post it's got to be sort of flawed somewhere
At least it gets the discussion sorted out or closer to that anyhow.
THE IMPORTANT PART:
And if you have a setup and current combination you like the sound of that's what all this hobby is aboutdone deal . but if we are going to start looking at the
deeper technical sides then we get into all this.
Doesn't change the fact you personally like the sound you got goin' on.
I am really curious as to the suggested DAP's and what the Original Poster decides on.
damping factors are also sort of explained here too among other places
http://www.head-fi.org/t/253489/ultrasone-proline-650-mods/60#post_3235914