Any one out there with an '09 Frontier ever added an aftermarket amp and sub to the OEM 6 disc radio? I'm not at all pleased with the stock stereo. Infact, it sounds muddy and is missing in the MID frequencies and missing BADLY in the highs. The "sub" section is a joke as RF put 2-5" spkrs. they call subs in this system. I have an '09 4x4 crew cab. Any input?