Luked, get an Art Pro Audio CX-311 electronic crossover ($109 online), and feed it from your preamp via Y adapters. The CX-311 has a dedicated subwoofer line output with adjustable frequency and level pots. I own two CX-311s.
1 preamp out to a 2nd preamp in any harm?
I have two preamps and would like to run the feed from one preamp to the input section of the second preamp and from there to a monoblock amp to drive a subwoofer. I do not know if there is potential damage to any of the equipment by doing this. Or is it better to get two y out from the cd player with a feed to each preamp?