I keep playing around with various solutions, but still haven't found anything that could be called 100%. Firstly, I've been using MP3Gain to change the volume level of my MP3s in a basically lossless manner (it just changes the frame volume setting without reencoding) but this is kind of a pain because I have a few other formats in my library still. Well, I primarily use PowerAmp and it recently added ReplayGain support, but... Something is just plain wrong with its ReplayGain support I think. It seems to be lowering even things that are already set to 89dB thanks to MP3Gain for starters (and the ReplayGain tag basically says +/- 0dB or at least it's no more than 1.5dB when it says to change it -- yes I remembered to remove the ReplayGain tags and rescan all of my collection after changing the volume via MP3Gain and it's worth noting that Foobar2000 on my PC has absolutely no trouble whatsoever.) Worse, the whole point of using it was to try to get it just right, so I add just a bit of gain (initially +3dB, but I think I've tried other values trying to get things just right) and it just seems to be way off. Regardless, I just haven't been able to find a value that's quite right for dealing with the issue either positive or negative. (And negative has its own troubles since it means I have the volume maxed or close to it and then something else blasts my ears at full volume...)
So more recently I got the idea to try one of those in-line volume controls. It's nothing more than an audio tapering volume pot and two 3.5mm connectors (one female with at least the decency to be gold plated but as it was soldered into the board and there was very little room to work with I left alone, the other I replaced from the original low quality connector and cable to a very short bit of Canare L-4E6S + Rean 3.5mm male connector.) The problem is, I ended up with roughly 200 ohms being the "just right" volume setting and that wasn't even far down on the pot. Unfortunately, the end result is a sound where the bass is bloated and just plain bad, the mids are recessed thanks in part to the bass, the highs are pitiful, and the soundstage is basically gone. Well, it's not meant to drive these headphones through what ends up being an impedance adapter. Regardless the result was horrible.
I've also tried third party apps that try to take over the volume control and give you a finer control including the demo version of a commercial one that people in forums such as XDA Developers have claimed actually worked. Nope. The result there was actually kind of interesting. It not only didn't work, but it seemed to actually be rounding to the OS's nearest value and pretending to give me a fine control instead... Frankly I'm just not sure that there is any way such an app can actually give one such control as it gave me the impression that basically the OS was overriding it in the end and that while it surely thought it was doing something it wasn't really.
I just can't seem to get through to any of the people on the software side of things. I've suggested to the author of PowerAmp that the program should have its own volume control to compensate for the crappy OS volume control, but no response. I've suggested in the CyanogenMod forums (I'm not sure where else) but only one person responded and that just to agree. No one seems to even be really looking at the suggestion, but then it's forums, not any proper suggestion form. Which is just pitiful because CM has generally always been good for compensating for these types of things that Google misses. Really I don't know what else to do though.
The whole situation is pitiful. How in the world have they managed to go through so many years and so many versions of Android with this horrible volume control? I know it at least dates back to Android 2.2 because I used to have an Archos 43 with the same issue. Ok, I understand that in the past people weren't really using them for music a lot, but these days a lot of people do and it can be a pain to carry an amp with you all the time. (Besides, why in the heck should I have to use an amp when it can drive my headphones directly perfectly fine AND I like the sound? It's just wasteful...)
Anyway, is there any solution left to try that I haven't thought of? My SGS3 is running CyanogenMod, so suffice it to say that it is definitely fully rooted to the point that I can even remount the root and system partitions as writable if I want to, so I can do just about anything in that respect, but at this point I can't find any other options to try.