don bother with the e5 it doesnt really improve things. What u need is a dac & amp.

@agnaem

Yes e5 do make a little improvement to the headphone but what I mean is...instead of wasting your RM90 on e5, its better for you to save up some more and get a better amp like hippo box or linearossa line W1 or any amp sub RM300 in the market.

Any superlux headphones are really need proper amping to make it sing well.

my two cents.

HD668B user here, bought it second hand. sound is superb, mainly used for movies + songs. now can turn on full blast in the middle of nite without disturbing others.

Seriously that small? 
And what its retail price?

Dangg. That is quite expensive.
I'll just wait for Superlux's portable amp to come. But dunno when.   
Affordable perhaps 

Actually I already owned an FiiO e5. 
But the bass boost is not as I expected. Aiyoo. 

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Added on May 13, 2011, 10:09 am
But it's not portable. 
Maybe I'll wait for IsTheTime 's reviews for that FiiO e11, if it's good (or great  ), I'll buy regardless to its price. Hehehe 

*Edit* Someone please answer    : And another thing, these 8 speaker-like holes at the cover of my HD668B's earpads? They didn't bring nuisance to people around me right?