That's encouraging to hear about the earhooks, I'd definitely like to be wrong. What makes you say that though? Like what are you basing it on?
The link regarding the G3 isn't about the sound quality, but the phone's behavior when plugging/unplugging cables (I replaced the jack years ago to fix that problem, and soldered it for good measure).
As it happens the G3 has a fairly good sound out the headphone jack, as far as smartphones go. It was the LG flagship when new, after all. I listen to and enjoy my Sennheiser MX985, Koss KDE250 and Audeze Sine headphones straight from the jack often, and the Sines especially sound fantastic there. I don't believe there's any output impedance related inaccuracy going on--it's never been a problem before, and the Ostry KC06A sounds about as good as it ever does on it.
I switched back to the headphone jack now to make sure I wasn't imagining things, but nope, same impression. I will add that it isn't bad in any objectionable way, and on second impression I can imagine lots of people listening this way without complaint. It's like how I loved my Sines with M4U earpads for months, but after trying them with Brainwavz angled pads, I can't go back. What the M4U pads that I loved make it seem dull and lifeless now.
This is kind of a generic guess, but maybe @16 ohms there isn't enough current available? The iSines do like quite a bit of power to be at their best. As an experiment I think I'll head down to the labratory tonight to build a cable with resistors on both channels, assuming I can scrounge up a pair with an appropriate value (do I need/want one on the ground line as well? I'll have to look that up). When listening with the MX985 and Sine, the volume is almost always maxed out, while the iSine 10 is getting uncomfortable at 3/4 the way up. I expect the results to be informative.