well.. here is my own personal experience and thoughts.. I have 3x portable amps (1 being a amp /dac since it is bluetooth)
first I have a very small portable amp a Firestone Audio Fireye mini.. it is tiny and sounds quite good.. I liked this as it was fairly unobtrusive and doesn't add much bulk to the portable set up... I haven't heard the E6 so I can't say how the sound compares?? and the Fireye doesn't seem to be all that available any longer..
at the same time I got the Fireye ...I also picked up a FiiO E11on a combo deal (current model is the E11K)... for me owning the E11 pretty much put me off all these larger portable amps/dacs you have to strap to your phone with rubber bands.. it is just super bulky and awkward... I just don't like it.. the E11 sounds better than the mini.. a little... but it doesn't matter the Fireye Mini was so much more convenient I would always take it with me instead.
Then xmas 2015 .. I saw the Elcom Bluetooth headphone amp /dac.. LBT-PAR500.. for me this was just the best... because.. I could use my ATH-M50 while out and about and not have my cellphone tethered to them.. the elcom supports AAC/aptX sound quality is excellent ..drives the M50's fine.. a bit under powered for my DT770 Pro 80's but does a better job than my phone itself.
The elcom has gone up in price however (maybe an old model now) at the time it was ~$40 but now is more like $80~ or so...
I realize of course at this point some would say well why not just buy Bluetooth headphones?? and fair enough.. However I'm very happy with the setup I have now with my M50's and this little elcom amp...
View attachment 890830
I would say I have found that for me I just have to the "hold" switch on as I bump the play button on accidentally entirely far to frequently.. but it is very nice to have good SQ with aptX and still be able to work my phone without a ton of stuff hooked up to it.