The DT990 pro version being offered is 250 ohm. But normally I only listen at a moderate volume (40-50%). At that volume will it be sufficient for it not needing an amp? It would be easier for me if I could just listen to it and judge for myself; however, the seller lives in a different city, so your advice is really necessary. Thanks!
By the way, before replacing the HI2050 driver, did you try removing the 4 white sponge pads inside the cups? I did write some of my impression after doing so, in the main thread for Takstar here http://www.head-fi.org/t/585356/the-takstar-technical-pro-gemini-greathon-cyberx-qpad-thread/2490#post_11015371. Wondering if you did and felt the same way as I did too?
Edit: My music are mostly metal/rock 320 kbps compressed MP3s. Only some classical stuff and DnB are in flac format.