ok fellas, I went to go buy/borrow some MB Quart speakers, but all they had were the Reference series component system in stock... they should do fine for the experiment's sake. the RSD216 woofer is the same size as the DSD216 and PSD216. the PSD216 might have a larger/deeper basket. I took my door panel off and it fits, but you will need a custom trim ring(made from wood) or you need to secure the speaker with metal brakets. When we installed QM215.61Q's we used metal brakets to secure it to the stock screw locations. I personally would rather router a wooden trim ring. The RSD216's came with the MB quart rings, which WOULD NOT FIT the area for the speaker at all. So the Reference, Discus and Premium lines should all fit the coupe area wise, the PSD216 should make the depth requirement also. All i need now is to borrow an E46 sedan so I can test the fitment. I'll have pics up shortly(waiting for battery to recharge).