help choose an fiio amp or alternative

[etaf]

I'm looking to replace a small cheap headphone amp ( runs on 2x AAA batts ) I purchased from Maplin a few years ago to run in the car and on a pair of headphones

used
On an apple Touch and a Nano
On Car Stereo via the Aux input - current amp works fine
in the car I also have a USB charger

Sennheiser PXC-450 Noise reduction headphones
Bass boast maybe useful - when on noise reduction loses a bit of bass

I have been looking at the Fiio E range and yep, a little confused

I would like to use while charging - I know some do - But if theres a big advantage for the modek that does not charge than happy to put up with that

I like the extended battery life 80hrs mentioned on one of the models

I will also purchase the ipod cable, as this is mentioned in a few reviews as improving quality

so what do i know
I'm tempted by the
E7 - £50
Batt life 80 hrs ,
no noise hiss,
can NOT be used while charging
150mW 16ohm

E6 - much cheaper £20 -
still no noise hiss,
can be used while charging
battery life 10hrs -
poor build quality compared to F5 - but F5 has hiss

E11 Approx £40
can NOT be used while charging
battery life 10hrs
battery that is easily replaceable
300mW - 16ohm - so is this really twice the power of the E7

E10
now very confused

so a little confused on what will work best

Do not want for PC sound - just the headphones

any help will help - thanks
also any alternative suggestions

[RobinHiFi]

The E6 sounds like it would work out really well - It is the best fit for the job, doesn't have features which you would pay for but not use, it is small and light. I Take your point about build quality, but I quite like the fact they didn't put it in a flashy metal case and charge twice as much for it, it is really impressive when compared to its predecessor.