I'm looking for a step up from my ~3 year old Sennheiser HD 203s - ideally the price range would be around $100-150 USD. They would replace my HD 203s at work and be primarily used to drown out office discussions (good sound isolation with little sound leak would be ideal). I'm relatively happy with the HD 203s, but I'm interested in jumping up to the next logical step. I hope to build/purchase a CMoy-based headphone amp to be used with the next set of cans, but that may be a short while off.
Primarily I use my business-class HP ProBook 6460 as a sound source - listening to music running the range from classical to punk, jazz to house (mostly v0, but some flac). I also listen to youtube, netflix, etc. I like the sound of the HD 203s after a few years of use - the bass is present but not over powering (depending on I'm listening too). I feel like they're maybe a little too quiet for some classical pieces. I'm relatively new to the hi-fi realm, but I'm looking for a set of headphones that I'll get another 3 years use out of.
I'm guessing for my requirements a closed-back, over the ear set would be best. As my Senn's have been pretty bullet proof, I've been looking at the HD 439s (currently on sale for $80 at Best Buy), or maybe the HD 518s. I've also been contemplating the ATH-M50s after reading the holiday buying guide.
Any help/suggestions/further questions would be great.