I want to add a sub but have no AV reciever

I have an HDTV in the living room but am not going with a home theater set-up. (That will go downstairs later) I would like to add a sub though. Is there any simple way to do this. Can I just buy a powered sub and attach it to my "audio out" on my TV and let the amp and cross-over in the sub do the work?

Thanks