Can I tap 12volts off the Gen 3 Prius battery for big stereo?

Ok. day 4, and all is still running well. My power plan is very over-complex, but it seems to be working, but I fear Im putting mega stress on the poor prius's buck-converter (step-down voltage side of its power inverter which makes 14 volts). It works like this...

1. 12volt marine battery in parallel with a 200ccAmp motorcycle agm battery, backed by a 1-farad cap, into the car.
2. car starts up, the accessory line closes a battery isolator relay (200 amp) that connects the subwoofer amp, and a 1500 watt sinewave power inverter in the trunk.
3. It also starts a time-delay relay set for about 25 seconds.
4. Frist 25 seconds everything is running off the car and these two batteries.
5. Once that relay trips, it open's the deep cycle battery, but leaves the AGM still hooked to the car.
6. The car's 12 volt side now runs the stereo parts in the trunk, only with help of the small AGM battery and the 1F cap.
7. The 120volt inverter runs a DeWalt $100 lead-acid smart charger, which normally sees a 98% full marine battery
8. its meter shows 10 amps, then 5, then 2, then 1, then "float" pretty darn fast (10 mins on a cold day like today (19f))
9. Meanwhile, the sub amp gobbled up power as needed to run 1 8inch dual voice coil in series, bridged. (not trying to blow up the c10. 10. The 120v also runs a small media computer with ssd drive, running kodi.
12. It runs a home theatre AVR unit too.
13. Things get really interesting now, but that beyond the power-plan.


Wth did I do all this? I wanted to recycle my old HT AVR, and figured it might run in the car, and yes, it does!
Then figured maybe it can do more than L R stereo, and yes, it does.
Then figured screw it, HDMI audio, DTS master audio, Dolby HD, the works....yes, it does, in a Prius and its kick nice person.
Added in a make-shift centre channel, dropped in some surround sound speakers, ripped out the factory radio (trash) and replaced it with a small 720p panel from an iPad. Ditched the wireless keyboard and built a custom wired kodi controller for the dash (ps2 to usb based).

Now I can watch bluray's in 5.1 waiting for the trains, and switch back to a sweet collection of DVD-Audio and DTS-CD's which work swell with Kodi.

 

I do know a thing or two about buck converters, and they have to work far less hard then boost converters, so while this is stressful run on it, in reality all that really means is that the IGBT's for the low voltage side need to stay "on longer" to maintain 14 volts. This is gonna make way more heat, and draw way more energy out of the 200V battery, ultimiatly meaning more gas is gonna be needed. Im ok with that for now.

 

Interesting, I found a wire that went "hot" once accy or ready mode was up (orange led on pts). I wonder if its a vampire?