connect sub woofer from preamp out on integrated?

A newbiew question. I would like to enhance bass to my 2 channel system by adding a sub woofer via Preamp out from my integrated. Is there any problem with that?
Indeed, that is very helpful. My Epos sub has hi and low level inputs/outputs (with a variable frequency cut off filter) and I think I am starting to understand what needs to be done....unfortunately, the Classe CAP 101 has pre amp out, but no Amp IN jacks....could I use the Tape IN jack instead of an Amp IN? Thank you for your patient guidance.
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Thx again for providing thid info. I probably need to re-think this system. Fortunately it is a second one.
I'm doing the same thing. Do I just need "normal" RCA-type cables?
I'm connecting a Vel' Optimum-10 using the preamp outs from my Cambridge Audio Azur 840A II. They look like normal RCA outs. Or, is there some sub-specific cable interconnect I should be using? Advice? Thanks in advance!
Oh.. My mains are Heresy III's, not sure if it matters. If anyone has similar experience, I'd love to hear starting points for x-over, et. al.