Ken, does your amp have the universal connector?
Is this the amp your sub has?
http://www.axiomaudio.com/gallery_display2.html?image=small_sub_amp.jpg&title=EP350%20-%20Back

Why not try something like this? This would allow you to use the phono plug. This would also be a pretty inexpensive option to see if the connector is bad, you may also be able to get one from a local radio shack or other electronic store.

http://compare.ebay.com/like/190607131040?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar