I installed a set of new components speakers and they sound so much better than my old coaxial speakers, even though I think my old coaxial Infinity Reference speakers were pretty good ones. The problem with coaxial speakers, however good they may be, is that it's really hard to escape the feeling that the sound is coming from where your feet are. This is a somewhat unnatural feeling. You want to be able to close your eyes and be able to imagine that the stage is sorta kinda in front of you. Separate tweeters really help with this. However, most component speakers just don't sound well when running off the head unit power. They have passive crossovers that result in some efficiency loss. When there are coaxial and component versions of the same speakers, the component version is rated to handle about 20 watts more power, but I doubt they get louder, due to crossovers. However, you can expect to get cleaner sound out of them. Most aftermarket head unit amps are rated at around 20watts RMS and that is most likely highly overrated. If the factory Mach or JBL RCUs are rated for 20 watts RMS (honesly) then perhaps 40-60watt speakers or components will sound fine out of them, but I would not buy super duper high-end 100watt components to run off an old factory RCU.