You can buy very long lengths of optical cable on e-bay. These cables vary in quality, but are quite affordable. My roommate purchased something like a 30 or 50ft cable for $40 to connect his laptop (built in toslink) to his receiver (an entry-mid level HK) powering a pair of Paradigm monitors (~$200 but I forget which ones). He has been playing compressed MP3s via this setup, but at this level the sound quality has been perfectly adequate (hooked up an AQ toslink as well and heard no difference). In the uncompressed file situation you speak of differences may be audible, but at the potential cost of your 35ft run it may be worth considering evaluating a cheaper cable (and returning it to ebay if it sucks).
Coaxial or Optical?
I'm looking for a very good external soundcard for the purpose of playing music through my stereo. The computer will be ~35 feet from my system. I'm going to run a digital out, at this length, is it better to use the coaxial or optical s/pdif? Does it even matter? These will all be uncompressed wavs or some other lossless compression so quality is important to me.