Thanks for the reply :-)
Being a bit of a noob myself wrt portabIe music, I will try the E07k, just out of curiosity. I am considering the E12, since the X3 amp section is somewhat better then the E07K as it is. I will ignore any general loudness difference. What I am interested in is gaining more authority in the lower frequencies, without having the music loud, and without using EQ adjustments.
In your case, I suspect that the increase in loudness you are experiencing, is due to the large difference in Line Out voltages between the X3 and Apple devices. Apple device are known to have Line Out voltages considerably lower than the 'standard', which is about 2 volts. This has been discussed elsewhere on head-fi, by people connecting X3 to car audio devices etc. It would seem that, since the emergence of Apple DAP.s etc. may manufacturers of car audio products have implemented an 'Apple compliant' Line In, rather that stick to the proper standards. This will explain differences in loudness between devices connected to your E11 Line In.
The velcro strip is a good idea :-)
Get back to us about the difference. The numbers stated on FiiO's website has the E11 as much weaker than the HO of the X3 and yet it seems to get much louder than the X3. I would say, based on what I hear, that the E11 does add some more impact to the bass over what the X3 does (I often run the X3 at +3 on the bass; would seem like the E11 has the same 'hump' with it set to 0 on the EQ switch).
In regards to the velcro idea; I enjoy finding ways to repurpose items. I say it's because I'm frugal...the wife says it's because I'm a cheap bastard.