R emember when 8-Tracks gave music lovers the freedom to take their tunes on the road? How about when quadraphonic sound was poised to replace stereo?   Maybe you missed out the first time around, but now you can relive the glory days of these defunct technologies.   Enjoy the soothing sounds of 8-tracks. Rock to reel to reel and surround yourself with quad.   Need equipment?   You'll also find classic components, car stereos and receivers.   Plus, free advice from Dr. 8-Track and free classifieds!   So, take a trip back in time and Keep On Trackin!