| You do not need to replace the HU, since when disconnected from the H/K amp it's a standard Boost unit. Of course it has no RCA outputs, so you might want an aftermarket amp for that reason.
The speakers are quite special to the H/K amp - for example there's no crossovers for the door speaker "woofer" and "mid/tweeter combo" (it's internal to the amp); and the rear speakers are dual voice coil.
You would really be planning on replacing all the speakers, if you put in an aftermarket amp. Be prepared for it to be louder, but have less clarity (unless you go to a very high end audio shop).
Ian C. Gloucester, MA, USA (UK expat) driving GPMINI or a non-MINI!  | 
