I need a 20 or 25 foot headphone cable

Do you want an extension or do you want a 20-25'er that goes in one piece from the driver units to the amp? If the former, they are available lots of places. For the latter, it would be available from many diff. aftermarket cable vendors, such as Cardas, Moon, Equinox, Clou, etc. For a description of the sonic and ergonomic diffs, try head-fi.org.

thanks Swamp...I guess I never thought about just getting an extension...that'll probably be easier & cheaper. take care.

Its called a headphone extension cable .Available everywhere.E Bay,BB,CC etc.Very common item.

I use a 20ft. Stefan AudioArt Equinox cable with my HD 600's. Prior to that I was using a 10 ft Cardas cable with a Grado extension cable. I would try to avoid an extension cable if you can. The weak link is the connectors in the cable. You're much better off with a long cable (no additional connectors). But once you plug them in I would leave them. Plugging unplugging, plugging unplugging, etc. will take its toll on the 2 prong pin plug to the headphones. BTW, the Equinox cable was a big improvement over Cardas. It's pretty expensive, and a long wait to boot, but worth it IMO.

Drew at Moon Audio will either make you a Senn cable that is long enough for your purposes, or sell you a headphone extension cable. He makes 'em in three varieties I think and they are all of excellent quality. Not a long wait either. http://www.moon-audio.com/
Personally I would go for a long headphone cable, not an extension, as I tend to accidentally pull the plug out of the extension if I move around or lean over to pick up the remaining sections of newspaper I am reading etc.