The preamp and cd player were both powered at the time (ie, both were "on," but not otherwise in use).this has always been a BAD idea & always WILL be! Switch off all your electronics & change the cabling - don't try to take a short-cut - you will eventually pay the price & end up spending a lot money repairing the unit due to sheer negligence...
If your equipment runs fine (which I'm thinking it should) take this as a warning from your equipment & never repeat...