How big of power wire do You think I will need to run both of these amps??
The 475 will power components and the 400 will be bridged 4ohm on a sub.
I think that the manuals says 4gauge for each so should I run a single 2 gauge and then split it off?
They will be in the back of a Mazdaspeed3
ZX475Ti and ZX400Ti Power Wire
Looks like you got it right 2 or 0 gauge split to 4 gauge for each amp. You can use the guide on page 5.
http://download.phoenixphorum.com/Manua ... manual.PDF
http://download.phoenixphorum.com/Manua ... manual.PDF