For my 2009 R55 with HIFI stereo (10 speaker option before they came out with the Harman Kardon version). Thinking of getting their speaker upgrade kit which includes new 4” door midranges and new a pillar tweeters. Easy plug and play. Anyone tried these? Is the sensitivity at least as high as the oem drivers? Also thinking of replacing the lower door woofers with Polk MM6502 ones to improve the bass. Not considering a subwoofer. Will leave the rear speakers the same - don’t think it’s worthwhile to change them. Any thoughts? Keeping the stock head unit and amp.