I owned one briefly and they sounded very good. Too bad they killed my ears after 5 minutes so I got rid of them.
If you have Portapros/Sportapros, or UR40s, remove the clips and snap the KSC75 drivers onto the Portapro/Sportapro headband or snap them into the UR40 driver housing,
Also, if going the PP/SP headband route, PX200 earpads would improve comfort as bit as well.
If I end up getting some PPs of my own, I plan on sticking their KSC35 drivers into my UR40's driver housing and either recabling the KSC50 drivers outta the UR40s or getting some KSC75s and sticking those onto the Portapro headband along with some PX200 pads.
Most likely the buy-KSC75s-and-stick-them-on-the-PP-headband-along-with-some-PX200-earpads route. That way the darker and more refined KSC35/Portapros will be in a full-sized circum-aural openback enclosure that's comfortable as hell and the brighter KSC75s on the smaller and more portable supra-aural Portapro headband while still using comfortable earpads.
In addition, the foam pads at the back of the UR40 enclosures would be removed, opening them up a bit, probably improving soundstage, and exposing the blue Portapro drivers, which would actually look kinda cool showing through the silver mesh, would give them kind of a mini-me HD650 look in a way.
The KSC35/Portapro powered UR40s would be used at home most likely with my computer, and the KSC75-powered Portapros would be used on the go with a Sansa Clip+.