Kuna, ID
Hey dudes.
You can control the balance between the backbox and cabinet speakers with the balance menu setting. I believe all of the Spike-2 systems have this feature. Also, Spike-2 is Stereo (SAM is mono) which means you can run either 4 Ohm or 8 Ohm, cabinet or backbox speakers regardless of trim pack. I've seen some mention of guys running a dual voice-coil cabinet speaker using the stock amp (i.e. from the MPU board). This is a no-no if you run 4 Ohm voice coils in parallel because you'll be presenting the amplifier with a 2 Ohm load and this will likely cause heating and premature wear-out of the amplifier section of the MPU board (a.k.a. the de-rated clock radio amplifier).
Finally, totally agree - PinWoofer is the way to go! 
