Of the Top Universal IEM, which is easiest to drive?

Well, I don't think it will change anything. If you use lower impedance heaphones, they will drain more power from the amp, even at lower "numeric" volumes (i.e. 15/30).
Frankly, I don't think low sensitivity impact much on battery life. Moreover, Triples are pretty easy to drive, so...

Just get a cheap amp......fiio e5, or something a little better.

I find that the ipod touch drives the TF10 well enough for me. The SE530 is a more efficient IEM but I prefer the TF10's sound signature. If you enjoy the sound of your TF10, maybe you should take tsne's advice.

The Zune must have some miniscule output or something, because the Sansa fuze by itself really can put volumes to a deafening level IMO.

I thought that the zune hd drives them pretty well. I had the bose IEM and no PMP could drive them loud enough for me.

My TF10 get really loud through my iPod. In fact, if I'm trying to fall asleep or need really quiet music I can turn it to the absolute minimum volume and be fine (if there's no background noise).

Dynamic IEMs are almost always easier to drive than balanced armatures. From the current crop, that would mean the IE8, or one of the monster turbine pro incarnations.

I have TF10's and a Zune 80gb, Fuze, and iPod video (the cool black one). They ALL drive the TF10's to absolutely dangerous, deafening levels. The Zune80 is WAY too loud at a third of the volume bar. Sure you don't have the airplane attenuator plugged in?

I must take issue with that.......... I find it simply not true. The se530, TF10, are easier to drive, play louder than the MTP at a given volume, even my orto's play louder at a given volume than any dynamic driven iem I own..which includes the monster and senn's

Actually, OP Is your Zune HD new enough to return, you may have a defective unit.
Seems to be an issue with th HD fairly often, However, I can tell you that a touch, or Iphone plays louder than A zune hd, as do the older zunes, still can't imagine a properly functioning unit not driving your triples pretty darn loud.
Edit: just for grins tried it..... either you listen louder than anyone I know, or something is wrong elsewhere.

With the TF10 rated at 117dB/mW the Zune HD must have a weak output , be defective, or you could be ruining your hearing in a hurry!

If I REALLY want to rock out with my Cowon S9, I will crank it up to 25 (of 40)... but usually my listening is around 15-17, or less. I have no idea how that compares to your Zune, but something definitely does not seem right here!

Let me rephrase what I said. Yes, it is true that some balanced armature phones can get louder than a dynamic iem. But I don't think there is a dynamic IEM out there that can't be played by your typical portable player, even low power ones like the clip. And unlike multi-armature iems, dynamics can reach their full potential without having to lug along an amp. For some reason the specs on many BA phones are misleading, maybe it's the crossover...not sure really.

I'm not even sure what you're trying to say here.

I don't think it is defective. Mine is about the same. 25 is about the threshold of hurting and 20 is just barely loud enough (for me)