lots of tech talk.. i don't ever hear anything about stereo upgrades. have you guys done anything special to your car stereos?

i suppose i'll start:
head unit - clarion DXZ845MC
fronts - focal PolyGlass 165V2 components
rears - JL audio components
sub - focal PolyGlass 33v2 13" woofer
amp1- 4 channel Kenwood Excelon KAC- X811D
amp2- monoblock Kenwood Excelon KAC - X541

currently debating building a box in place of the spare tire.. has anyone done this or have any input on whether this is a good idea?