Upgrade from Sennheiser HD25-1 II

I'd say the Fischer Audio FA-003. It's got a big soundstage for closed cans, and it's also really neutral (the main selling point, actually). They usually go for about $180 and sound great unamped.

 

But like most headphones, they are even better when amped. With the extra $120 left in your budget you could get yourself a nice portable amplifier. 

Hmm, that's not very easy; you already got great closed headphones and it's not easy to incorporate all of your wished into one closed model

 

AKG 271 could be an idea, but I'm not sure they will be a definite upgrade to HD-25's, same goes for Beyer DT1350

 

I think to have a definite upgrade, closed, not very coloured, you would have to go to Beyerdynamic T5p, which are way out out of the budget.

 

Anything within your budget, I'd personally consider a side grade to the fantastic HD-25, in stead of an upgrade.

^ I didn't hear 1350's so don't know, but I think they will definitely benefit from ampage, like most if not all headphones in this price range. Your HD-25 would also benefit seriously from a 100 bucks portable amp

 

I'd look into 271, 1350, but I would spend some money on an amp, which brings you an upgrade from the HD-25's you already own, as well

Don't bother with the Audio Technica M50s, it would be downgrade as the HD25-1-ii's are superior in every way. Watch Jude's review of the Beyerdynamic DT1350s on Head-fi TV Episode 4 (he compares it with the HD25-1-ii's):
http://www.youtube.com/watch?v=Aahpv0_DDFE

Definitely try the DT1350. It will sound brighter, but adds resolution. It fulfills all your points on the list.

 

There really is no upgrade for a Sennheiser HD25 unless you're willing to greatly exceed your budget, as someone else said.

 

Recently I felt the need to add to my headphone collection, because my HD25's were kind of unfulfilling in some ways. I picked up a pair of AKG K240STUDIOs, which have really filled the gap. But I still need an amp for them.

 

If you want to take the DJ headphone rout, you could go wit the Ultrasone Pro DJ 1's, which are about 234USD market price. I don't know anything about them, though, and so I can't help you there. And again, these are DJ headphones, so they are somewhat specialized and probably not made for only listening. But they're Ultrasones, so I doubt they'll disappoint.

 

LOL, I like that sentence! :) Weird enough, it seems Ultrasone is more popular in the US than in Germany, hehe.

 

However, any Ultrasone will not be an upgrade for this demand: "neutral sounding headphones (sometimes the Sennheisers seemed to add some coloration to the midrange, which I did not care for)"

For what I read about 1350's sound signature and after experiencing T50's, I think iBasso T3 could do very well; it's small, light and a little bit warmish, which both HD-25 and 1350 could use.

 

^ don't know, sorry

 

I auditioned the T3 only paired with T50's, HD-25's and ESW10jpn, didn't hear any hissing

I've never read about any hissing problems, but after reading your situation the T3 was also the first thing to come to my mind.

SRH840's do perfectly fine unamped. The dt1350s are also a great option but i doubt theyre different enough to merit having both... The 840's are very laid back smooth and silky which is a stark contrast to the hd25's in a good way. It's nice to be able to have two completely different headphones sometimes, makes you appreciate them more. I really want a pair of something that's the complete opposite of all my Shures and I'm thinking the HD25 or DT1350 would fit the bill perfectly.