Had my uprev on 90k and the diffeence was very good indeed , depends what suporting mods you have done though.
Its not about extra BHP its about torque and full throttle
The RCA boosters only increase volume if that's the issue.
Changing the HU doesn't improve tje sound greatly just adds funtionality and connection options, to get a better sound you need to be looking at new speakers and new amps
If your not to sure what you are doing maybe find the guides and show them to whhoever fitted the unit, everything works now albeit not 100% you could end up messing something up...
Buster has done a guide on stripping the RCA wires to increase volume, it's because the Bose amp runs off a very high level. It should be in the ICE section
Ok, the gear surround just pulls up, put your hands through the gaiter annd pull up.
All depends how they fitted the HU though,
they could have fitted the cage to the car (easy) or to the actual fascia (more difficult)