How to hook up a subwoofer with an integrated amp?

I am quite happy with my current 2-channel system, but given that it's driven by a tube integrated (EL34) amp, I have been thinking of adding a good quality subwoofer to enhance the bass department. The question is: how do I hook up a subwoofer with an integrated amp since it doesn't have a sub-out?

Should I:

(1) use Y adapters for each channel to split the signal from the cdp to both the sub and the amp? (cross over concern? degradation of signal to the amp?)
(2) long interconnect to go from cdp to sub's pre-in, then pre-out to the int. amp? (using sub's cross-over, but not prefer due to long I/C's)
(3) Speaker wire from amp to sub, then sub to speakers? (any cross-over concern? degradation of signal to the speakers?)
(4) Any other ideas?

While we are at it, what would be a good quality sub (hopefully under $1,200 used) that goes well with my system:

VAC Avatar Tube Int. Amp
Sonus Faber Grand Piano
Cary 303/100 Cdp
Nordost Blue Heaven Bi-wire spr/IC

All input would be greatly appreciated. Thanks guys!