I'm looking at upgrading or replacing existing speakers and/or amp in my BF II with Premium Sound.. the rear sub distorts bad when volume is up high... with medium volume it all sounds normal, just high volume kills it...

Is it possible to upgrade the amp and speakers without too much hassle?

Is it worth replacing the sub with another factory sub or better to get an aftermarket one - but will it fit without having to cut bigger hole?

I'm also looking at adding bluetooth for the stereo to stream from my phone - any recommendations on a good bluetooth kit to suit?