just got a 2017 GS 350 after driving a 5 series BMW and unfortunately the car I bought didn't have the upgraded sound system. I got spoiled by the BWM system and want something close to that now.

If I just upgrade the speakers with aftermarket and leave the head unit alone, is there enough amp power from the stock unit to make the switch to upgraded speakers worth it? I'm not looking for booming bass just better all around sound.

If an aftermarket amp is needed, any recommendations without breaking the bank and are there any size/depth concerns I need to be aware of when buying replacement speakers?