Has anyone put 6.5 inch subwoofers in the soundbar? I'm not using an amplifier so it would be whatever wattage the head unit is putting out. I have a Kenwood DMX7706S head unit. Specs say the head unit has a built in amplifier 22 watts RMS/50 peak x 4 channels. My thinking is there are tweeters and midrange speakers on the dash, so there should be subs to handle the lower frequencies. Any thoughts on this?