[moleface]

My Sennheiser CX400 IEMs gave out recently and I'm currently into the first week of my Nuforce NE-6s.
 
The CX400s had a really nice smooth warm bass-heavy sound to them. The Nuforces are definitely more detailed than the CX400s, but I've noticed problems with bass. 
 
The problem wasn't obvious until I started listening to a lot of late 80s/early 90s hip hop with a really thick full drum sound - all stuff my Sennheisers handled perfectly. The bass distortion on the Nuforces is subtle, but I can't stop fixating on it once I notice it.
 
Before the Sennheisers, any headphone I tried in that price range always got a noticeable clunky overloaded sound when bass got too heavy, particularly on drums. With the CX400s, I was very pleasantly surprised to find a pair of budget headphones that played those frequencies without distorting. Is that considered unusual for this price range? Was I just expecting too much of the Nuforces to handle heavy bass without distortion? Is this how headphones in this price range tend to react to bass?
 
I'm listening to music through a Sansa Clip with Rockbox firmware. I've tried turning the eq to flat, and the problem diminishes but doesn't go away.
 
I've also noticed my ears ringing after using the NE-6s, whereas I never got that with my Sennheisers. Maybe the drums are distorting because I'm turning the volume up too loud to compensate for the lack of a proper seal? I do tend to listen to music too loud, though that never gave me ringing in my ears with my previous pair of IEMs.
 
Has anyone had this experience with the Nuforce NE-6s?

 

[moleface]

After further listening, I think the "problem" is that the NE-6's bass is a lot more detailed than the CX400s. I'm used to the smooth rounded bass sounds of the Sennheisers - the NE-6 has more midbass and the bass in general has more of a texture to it. The rest was the placebo effect - it turns out that the tracks in question have the same drum "distortion" on my Sennheiser 555s.
 
Comply T400 foam tips deepened the bass and rounded off the initial harshness to the treble- I actually had to eq the treble back up to compensate. Now I'm hearing details in songs that are barely audible on my other headphones, without any harshness - nice. The temporary tinnitus is worth it to listen while they burn in.