no, the amp is not necessary but BOSE is known to do quirky things in regards to speaker resistance etc. So you'll want to know the speaker ratings to match an appropriate amp. More importantly, the '03+ systems use the MOST fiber-optic set up (the amp is a part of this loop). As such you'll either need to find a MOST compatible (difficult to do) head unit or just plan on replacing h/u & amp. And that takes you back to the speakers which you may want or need to scrap so everything works and is mated well.
Good luck
