I purchased my Yamaha 8" YST-SW215 as a stand-alone sub 25 years ago and it has ins and outs. It is now connected to my computer amp. I have seen other subs, usually, or always older ones that have them and were also not sold as a surround package. I would never, on purpose purchase a sub from a cheap KMART selling surround system. I was duped by the JBL brand on the sub I almost bought. Funny thing is is that it didn't dawn on me that I didn't need to buy one anyway, after trading the subs room to room. TLS Guy saved the day big time there. Although had I arrived there and looked at the driver I would have seen that it was not a 10" and would have passed. That is if the driver was exposed. He didn't have good photos.