You can get speaker to line level adapters from most car stereo shops or electronic stores that sell installation kits like this Invalid Link Removed or you can do it yourself
http://www.epanorama.net/circuits/speaker_to_line.html
Or a Red Box DI [Invalid or Expired Link Removed]

http://www.epanorama.net/circuits/speaker_to_line.html
Or a Red Box DI [Invalid or Expired Link Removed]
