So, I find that using the audio out port is awful in general. I was using the audio out cable to connect it to my vehicle and even at 100% volume, its terribly low. I like to put on some music while in the shower and I have a small speaker I keep in there, which is MUCH quieter with my LG G2 than with my Gnex. The audio output from this phone is just low when using the 3.5 mm output. However, i did get a new truck this week and with the bluetooth audio: its plenty loud: maybe 2x as loud. I had the volume at MAX with the audio out aux cable and it was not even that loud, but with blue tooth- I dare not turn it all the way up.
I did just try some headphones, and they were plenty loud: so it is just when using the audio out with my car, my Xmini speaker, or some other speaker that its low.