I have a HK AVR320 with 4 JBL N24 speakers. I need a sub. I received the SONY SA-WM40 sub recommendation but it is not available in Mexico. The only sub available is the SA-WM20 but I think I can get a better one. Which other sub is a good option? I have Infinity, Definitive, Marantz, and other good brand dealers nearby. My budget is more or less $400 USD. Thank you very much for your feedback.