Yeah, a professional shop would be best unless you are very confident in your installation prowess. Most dealerships won't install aftermarket speakers, so a whole system, most likely a no. Never hurts to ask, but their labor rate might actually be HIGHER than a specialty stereo shop.

You will need to run a power cable (usually 4 guage or bigger - use the equipment suggested size) from your battery to inside your cabin, make sure you use a proper sized fuse as close to the battery as feasable. You would have to do this anyway for a proper amplifier installation. The capacitor would then connect to the wire from the battery into its iput socket (instead of it running directly to your amp or your distribution block if running multiple amps). Then you use the output socket(s) to run the power wire to your amp. The capacitor also needs its own ground, the upper models will accept your amp grounds (up to 3) on a negative input terminal so you only have to worry about grounding one wire in your cabin.

It is simple (but not easy) if you know what your are doing. You find a grommet on your firewall that is big enough, or drill one where there is nothing to hit and use your own grommet. Removal of some trim pieces to lift up the carpet, etc. It will look clean and be basically the same thing as having it done professional without the cost.

A big thing to watch out for is whether or not the shop will cover any damage THEY do to your car. Even if they say they do, have pictures before you go in as proof. I know I was told by a major chain if they installed a head unit they would not replace any parts if broken because the pieces were known to break before. I thought there was insurance for such problems, but I didn't argue ...

I wanted to upgrade and didn't feel like sweating in the heat to install it myself. I ended up just keeping what I had, which wasn't bad in the first place. 88 RX7 GXL, had CD and a 10 or 12 band equalizer, and it had its own amps on all the speakers.