Do you find that your 250ohm model is as rolled off in the highs as the 80ohm model? I had no problem with the bass when I had the 80ohm version, but the highs were quite lacking compared to my akg k240DF which was my reference at the time. I removed the foam and replaced it with thin cloth and was able to get more treble that way, but it still seemed a bit rolled off. that was my main issue with them other than the fact they didn't fold up for portable use.
I have had no issues with rolled off highs in either 80 or 250 ohm headphones. then again, I ultimately got rid of both pairs of akg k701 and both pairs of akg k601 I had because try as I might. could never get used to the treble, they sounded notchy and boosted - I hated it.
dt-250's are just neutral to me.