I got these small 6 inch subwoofers with big magnets and when I hook them up to a car stereo the bass is nice but the voice is muffled, can I just add tweeters to make them in to 2 way speakers if soo how? Also I'm just using the 2 front 50w channels on a Kenwood Bluetooth car stereo. An I was also wondering if there was a way to make them marine safe just wondering. I got the subs for free and not trying to make a full blown sub amp kit.