Well I got my fii0 E5 in the post today... and YES!! This gives that added bit of oomph I've needed with these 'phones
The sub is definitely there with the "bass boost" feature and I get that extra bit I was looking for.
The bass is really good on these earphones, just slightly lacking in sub bass, that's all and the overall sound is amazing.
For anyone else who finds this, I do recommend one of these little gadgets, very helpful.
Although If I'd have known about the lack of sub bass, I would have probably have opted for another set of earphones... I don't think spending extra just to get the right sound is really a thing you should have to do, But, you live and learn.
My "Chill-out" playlist now sounds as it should and the extra low end is present and correct.
Enjoy some chilled music. (With serious sub bass)
http://www.youtube.com/watch?v=7Y-UJDrfxrM
http://www.youtube.com/watch?v=Vz0en4xb9Ds
http://www.youtube.com/watch?v=ccqY-R_M2nY