Two days ago I got my new pair of Sennheiser HD 449 headphones. I've been breaking them in with a large variety of music on a repeating playlist, and they probably have about 24-ish hours of break-in on them now. When I first got them they had absolutely no bass, no mid range punch or weight, and sounded tinny like a cheap boombox. I read online that they need up to 70 hours of break-in time to sound their best.
After the 24 hours of break-in they've improved some with respect to bass and midrange punch, but they still sound rather dull and flat. Detail and clarity is good, but otherwise these are completely underwhelming headphones so far. These don't sound warm at all, either. My previous pair of headphones was a set of $40 Koss Portapro which are highly acclaimed to be an amazing value. I was pretty happy with them, and felt that they were airy and relatively bass heavy (bass on those could be a little muddy and overpowering at times) with a warm overall tone.
I'm not a bass fanatic and I don't listen to dubstep, rap, electronica, house, etc, but I like a solid bass punch and right now these Sennheisers don't have nearly enough low and even mid range punch. The low end is severely lacking unless you turn them up loud, at which point the highs become harsh and piercing which makes them unlistenable.
I've tried driving them with my Creative onboard add-in soundcard (X-fi Titanium) and my Van Alstine hybrid tube preamp. I listen with uncompressed .wav ripped from CD's, or from a CD player with external DAC. Using my Van Alstine preamp, the headphones sound better in the way that driving any kind of headphones or speakers would sound better when using better equipment. Bass and midrange didn't really fill out any more on the AVA preamp.
So my question is, anyone with experience with these or similar Sennheiser headphones know if they're going to get better, or should I just start looking at selling these and finding something else? This is most definitely the wrong place to ask but I don't belong to any audio forums.