I bought the PAC aux input when I first bought the car. It lasted a whole 6 months... after doing some research I found that almost ALL the stock/OEM radio adapters (even the actual Mazda part) don't last very long (i.e. a year or less)...
If you're already looking to replace the speakers than do yourself a favor and just replace the headunit to. It's not hard (takes 30 min or less). Crutchfield will include all the adapters and wiring harness for free. I bought a JVC double-din unit with and aux input for around $100. Replaced it before the speakers arrived and was amazed at how much better the stock speakers sounded. When I got around to replacing the OEM speakers I was shocked at the difference (and I thought the factory sound system was pretty good, and it is for a OEM unit).
Also if you do your research several AM headsets have adapters that will let you keep/use your steering-wheel controls (was a BIG sticking point for me, but my JVC is fully controlled by the SW controls).
