I use the Senn HD280 at work for quiet listening (work in a mostly quiet office) and I think they sound great with many types of music, so depending on your music preference.... I will mostly listen to acoustic guitar/vocal (Andy McKee, Jack Johnson), electronic (Aphex Twin), trance (Armin van Buuren) and metal (Dragonforce, A Life Once Lost).
When listening at low volumes, the highs are very precise, great for acoustic guitar, classical and most electronic music. The lows are barely there, but add a slight warmth for most non-bass emphasized music. There isn't a LOT of punch in the mid-bass but it's more of a laid-back punch, so depending on your bass-head-ness you may or may not like it. It sounds good for trance, to me, and the low end is filled nicely by most songs.
At low volumes, the mids sound very artificial and are lacking the synergy of many other phones, like the KSC75 you're used to. If you primarily listen to Rock, I wouldn't recommend the HD280 at all really
Mid-trebel is a bit recessed too, making some guitars sound a bit funky in soundstage, and almost a bit artificial. Depends largly how much the mix is dependent on the sound of the guitar to fill out the frequency spectrum in your music.
Upper-trebel the phones are very precise, yet smooth without the harshness (IMO) of the KSC75. Old school Metallica sounds excellent on HD280s.
Overall, I like the bit of laid back sound of the HD280 at low volume, as nothing overly sticks out, it's a very smooth sound until you get to the upper-trebel and get the nice sparkle that keeps your attention. This allows me to get my work done without being too distracted by the music. Hope this helps!