Well, I pulled the trigger, took PurpleAngels advice and went for the 250Ω DT-880.
I saw them for 233€ @ Amazon instead of 299€ @ Beyerdynamic, so I ninja-ordered.
Turns out that the X-Fi Titanium HD can power them just fine, no need for further amping at all heh saves me 500 bucks.
They were a little shy on bass, so I fed them +4dB @ 62Hz and +2.4 @125Hz and now the bass is like rolling thunder.
(Probably too much for people with normal hearing but I'm a little impaired due to scarring tissue on my eardrums.)
The 1Vrms or 1.4Vpp of the headphone out get me a nice volume, I can't reach my pain threshold but I wouldn't want to do that anyway.
Comfortable listening volume for long periods lies around 50%.
I'm very happy right now, being able to put the need for better audio equipment to rest and wanted to thank you for your input.
For $10 you could get two LME49860NA op-amps, to replace the two JRC2114 in there right now.
The LME49720HAs in the Titanium HD are fairly good and a little more of a hassle to update.