I found this under "Lexus Q&A":

Will a speaker make that much of a difference?

YES. Almost literally like night and day. Speakers are the weakest link in any system. Note...a Dynaudio equipped system with a STOCK Pioneer head unit will WASTE a Mark Levinson equipped GS. And not by a small margin either. I've visited 2 dealerships to let them take a quick listen on their ML system versus Dynaudio/Pioneer "Premium".
Verdict...Dynaudio/Pioneer beat them by a longshot. Wasn't even funny. First mod...change out those speakers.

My question is, does this mean just dropping in a new set of speakers without changing the amplifier? How about the subwoofer?

 

I have a question for you on the thread "After market Ignitions" please respond to it. It could be good for the forum.

 

i am not an audio expert but you will need to take out the stock sub obviously regarding your subwoofer plans. the new sub will require another amp. now you have a lot of bass....you will need better components to either balance out this large amount of bass...or to just upgrade your audio. if you drop in new speakers, chances are good they will be more powerful than stock, you will need another amp. you can hook up the new amp and theold one in serial by the way.

VJ

 

I recommend you post this question on the electronics forum so the stereo gurus can help.

Short answer. Swapping sub will probably require an LLC and an amp depending on the efficiency of the new sub. Stock system provides about 40 w rms to the sub.

Swapping other speakers to Dyns will work without additional amps as long as you don't expect loud volume without noticeable distortion.