Hi, Thor.
My research didn't turn up much info on the WWW with respect to those speakers. What I did find, though, was that they were sold as a system with a Kenwood amplifier. The amp had dedicated speaker outs for the subwoofer. You would run the wire from the amp to the speaker that had the sub in terminals. You then would daisy chain to the other speaker's sub-in.
You won't be able to do that with your Yamaha. However, the Yamaha does have pre-outs for the subs. What that means is that your receiver serves as a preamplifier when the pre outs are connected to amplifiers. Most people just connect them to active subwoofers and they are done. But you can just as easily run a cable from the pre out to pre in on any amplifier. Then you just connect your speaker wire from the amp to the appropriate terminals on the speaker.
You can either daisy chain or use an amp for each sub woofer. You can buy a pair of those chip amps; they're all over ebay. Here's a link to show you what I mean:
https://www.parts-express.com/cat/au...s-modules/3464