Your problem is that HTS packages (like the one those speakers came from) rarely come with self powered subwoofers. The sub amp is in the main unit.
AVRs never have subwoofer amps built in.
You will need to get an AVR and either an amplifier for that sub or a self powered subwoofer. I would get a new self powered subwoofer.
If you are not going to upgrade those speakers in the near future than I would not go for anything more than an entry level AVR. Onkyo and Yamaha are pretty good at that price point.