can you take a high res photo of the back of your receiver and post a link here (like on photobucket)
since the manual for KRF-V5080D shows sub pre-out
http://manual.kenwood.com/files/B60-5439-00.pdf
or you have KR-A5080 ? in the later case you'd have to connect speaker level outputs on receiver connects to speaker level inputs on the sub and from spk out on sub to speakers
This will complicate the connections, but you may not have a choice unless you get more modern receiver
You can find manual here:
Kenwood - Home Electronics Owner's Manuals