Pioneer HTV-2 subwoofer conversion

[bmxhacksaw]

I have an old Pioneer HTV-2. It is kind of like a Bose 3-2-1. There is a proprietary cable that goes between the powered sub and the control unit/head. I'm figuring that it would be relatively easy to rig up an RCA input on the Subwoofer to utilize it as if it were an ordinary powered sub connected to my Harmon Kardon Integrated amp.

Anybody know how I might accomplish this or can point me in the right direction?