ddawson24 is right, it's probobly safe to say that your Sony player have 45W - 65W per channel and if your speaker is at 4 ohms then you'll be looking at 4 amps per channel.
Rules of thumb: the wires should be 12% to 13% larger than the normal wire for marine application and should be UL approved marine grade wire, wire that is approved for the corrosive marine environment and charter boat service. this test insure that standards for moisture and oil resistance, cold bend, flammability and heat shock is meet or exceed.
Since Sony suggested the wire then you should be ok.
You can find the reading materials through marine wirrings or boat cables.
Check here:
http/www.awcwire.com/FAQ-Marine-Cable.aspx