You new HU will send the signal to the factory amp, so the speakers wont be getting anymore power without bypassing it first. That in mind, Alpine makes good HUs and Infinity speakers+basslink will round out the sounds nicely.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>