Panasoic SC subwoofer to non-Panasonic receiver/ampliifer

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I have a Panasonic SC-HT730 home theater system. Some time back, the amplifier/receiver/player had a melt-down, literally. I did not realize it would be virtually impossible to replace just the amplifier,so I trashed mine instead of trying to get it repaired. Big mistake. I want to be able to use all these speakers as I did before but I am having trouble finding a 5-disc 5.1 channel amplifier/receiver that is compatible with the Panasonic subwoofer. Apparently Panasonic decided to make their speakers completely incompatible with any other manufacturer. The cable that goes from the subwoofer to the receiver has a square end. While some older Panasonic receivers can handle this (I've only found used ones so far), every other receiver I've looked at cannot accept that square connector.

Is there any way to connect the Panasonic subwoofer to some other manufacturer's receiver? If not, I'd really prefer to buy a Panasonic home theater receiver that is new, not used. No matter what an ebay seller says, I'm doubtful that a used receiver that is several years old will work, at least pat the 30-day return window. Any advice? Thanks.