Subwoofer / Amp advice!

Hello! I'm inquiring about a Simple Home Audio set-up that I'd like to perform. I have Two J.B.L. Century L-100 MKII Bookshelf Speakers with slanted metal floor racks. I'm looking to power them up with at least 100-Watt Amp. I'd also like to Use a 12" Velodyne Floor Sub with this setup. What can you recommend? I have an old great working 1977 Sansui AU-717 Two Channel Amp & a TU 717 Tuner. But! I don't think I can connect it to the back panel (Floor Sub)? How can this be done? (if) at all.

Any recommendations on another Amp suitable to connecting with another sub-woofer.

Thanks. thechops