sorry no pictures of the install and everything else is stealth (at least as far as the interior is concerned). I have a nephew who is pretty into this stuff so I left most of the details to him. He is very detail-oriented and so it was a pretty involved install and he was committed to all solder connections and we had only one solder iron, so it was a lot of him doing the work.
It's a MY2020 BRZ. Stuck with the original head unit because I actually like it and it works fine. We ended up running all new speaker wire (StraightWire Waveguide 16/2 - $250 by itself).
It's a two amp system - Rockford Fosgate T400x4ad and a Kenwood KAC-M1814 4x45. The RF runs the bass speakers (door - JL Audio C3-650 6.5s) and mid (Eminence Alpha - 4inch - front dash) the Kenwood runs the rears (stock 3.5s - the 4 inch Eminence's wouldn't fit without significant mods and while I might change those out in the future, the stocks are OK for rear fill for now) and the tweeters (the modular tweeters out of the JL 6.5s).
The 6.5s just needed new mounting brackets. The 4's and the tweeters required some mods to the grill and the speakers to make work.
Everything runs through a Dayton Audio DSP-408. Since I have eight separate amp channels and have everything run through the DSP, I don't have any crossovers and don't use any filters on the amps (also have a used factory amp, speakers and tweeters willing to let go for a song.
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Put a TON of Dynomat in the doors and rear wheel wells and it makes a huge difference. The feel of the doors alone (feels SO much more solid) was worth it and I would do that mod even if I did nothing else. In fact, I put a couple of panels in the trunk just for the sound/feel of closing it - WELL worth it (not an autocrosser so I am not counting ounces).
I know some will question the lack of a subwoofer, but given the power I am sending to the JL 6.5's, and the fact that they don't have to do anything other than low end (as well as the fact that my music tastes don't tend to run to "bass thumping" music), I am pretty happy with the results.
I really like that it's stealth - no way to know that it isn't factory without lifting up the trunk mat. Did lose front/back fader functionality from the head unit, but the DSP has bluetooth and a phone application so that isn't a huge issue. Still working on some of the fine tuning on the DSP, but pretty amazing little upgrade.