I have a
Pioneer Laseractive, but never figured out how to control it
 serialy without the PC command module :( 
 Is that hardware that's missing from
your player, or some sort of
 software package for your PC? 
 
    The laseractive is a laserdisc system with game modules. You have a Sega
CD pack, a Pc Engine pack, a Karaoke pack and the rarest of all, the PC
commander pack, where you had a serial port. Of course, you can find some
schematics of the game packs, but nothing about the karaoke and pc modules.
    Maybe someday... :)