Just some food for thought. If the the house (stereo) bank will be connected to a dual battery switch and used to start the engine on occasions, keep in mind that a typical V8 engine starter can easily draw 250A.
I'm using 4awg for switch connections and 2awg for bank grounding connection and starting bank to starter connection with no issues. It all depends on your setups draw. Blue Sea has a sizing chart for awg and fuses.