Look, the Bose amp and speakers are garbage. Don't get me wrong, they have some nice systems, like on my new CX-30, however, the Bose system in the 2010 Mazda 3 is a cheap, lousy sounding system.
Your best option is to buy a compact 4-5 channel amp and replace your door and sail panel speakers with good aftermarket speakers. Place the amp under the driver's seat. If you want even better sound, add a powered subwoofer under the passenger seat. You now have a system that will sound light years better than the stock Bose system, cost less, and take up no more interior or trunk room. It will require a bit of wiring prowess, but it is not that difficult.
The Bose amp is not worth $50, let alone $900.
And lest you think, I am not a Bose basher. I own Bose speakers in my home that I like, and as above the CX-30 system is nice. But the 3 Bose system...it sucks!