Appreciate the advice received so far to avoid sticking with the stock head unit and using converters to add a subwoofer. Didn't receive any recommendations for alternative equipment, so I went with a Pioneer AVH-X5500BHS, a JL Audio HD750/1 (750 Watt Monoblock subwoofer amplifier), and 2 12 inch Alpine Type "R"'s in a ported "Fox Acoustics" box. Working on the install now and when complete, will be looking to upgrade the remaining speakers and adding an amp to power them. Not sure what would be the best option for replacements or what will fit but again, they are going in a 2009 Dodge Ram 1500 Quad Cab. Thanks again for the help!