Depends on the speakers, if you replace them with higher quality speakers that have the same Ohms and the same or higher Sensitivity, you could probably get by with the OEM Amp, but if you really want to upgrade the entire system, a new Amp is highly advisable...!
You'll probably hear a difference, but whether or not it's an improvement is a gamble. There is DSP that is adjusting for those specific speakers, so simply dropping in something else may or may not help. Either way, I wouldn't expect anything special from dropping in some speakers and keeping everything else the same.
Can’t speak on the drop in replacements as I’ve never used them but I’ve owned two Mercedes’ with HK setups and found it absolutely necessary to disconnect half of the stock plastic coned HK drivers and swap out the remaining with aftermarket speakers. The factory system sounded good when I first listened to it but didn’t take long to get the feeling that the overall sound was missing “presence”, about as accurate as I can describe, in the music I was playing which I guarantee is due to the excessively cheap and stripped down drivers that were being used by HK. Most drivers don’t even have a basket and the surrounds are molded into the plastic mounting brackets and were definitely designed to cost as little as humanly possible to manufacture so it’s no mystery why they fall way short from a typical sq setup. My first HK system I replaced the head unit and wired back into the existing wiring(which I stress don’t do or you’re going to have a bad time) but it was a 2005 Benz so a dash kit was available for an aftermarket stereo. My next HK head unit was built into the entire dash unit which didn’t make a swap out for stereos possible. If I were you I’d bypass the HK system entirely, get a dsp that allows for a direct connect to a portable source, Add an amp or two with all new aftermarket replacement speakers and enjoy from then on. Money is usually a factor in these decisions so that option may not be a possibility but even something as simple as adding a helix mini and running a two way front stage plus sub will get you that fullness and punch that the HK system lacks. The surround sound of the HK is nicely done and curious how well the focal drop ins match up to Eqing of the HK processor but something tells me probably not very well but worth a shot if you’re already thinking of trying it. Would love to hear your thoughts if you do end up swapping. The processing is spot on but sadly the drivers are straight garbage in the stock setup.
Hi all, I am going to go for the Focal ES 100k. i was wondering do i need to use the supplied cross over that comes with the speaker or would the HK amp wiring in door have a seperate wiring for tweeter and mid-range??