I am sure when I have my Evo 6, I fed the wire (more like a large snake) from the bulkhead through the front passengers side wing and then behind the glove compartment - the underneath the carpet to the boot.
My stereo wire is one over gauge. About 3 cm thick. (theres alot to power). You can feed it through the existing loom grommet near the top of the bulkhead on the passengers side. I used a reamer and a drill and drilled a new more accesible hole in my bulkhead due to boost gauges and controllers. Just make sure you cover it in Waxoyl when your done and put a fitting grommet in the new hole.
You can also go through another hole which is on both the passenger and drivers side that goes through the wheelarch. Only problem is then getting it out of the wheel arch!
Best way in2 the engine bay is thru the factory main wiring gland/grommet at the rear top of the drivers side front wheel arch. 2 get good access u will need 2 remove the wheel and wheel arch liner , then if u look up inside u will c where the main loom passes thru. There is an apeture in the inner wing near the front 2 get in2 the engine bay , u will c it near the power steering res.
2 get 2 the boot , use the drivers side , all the wiring in the car that go's 2 the rear is ducted near the sill under the carpet. U will need 2 remove the kick covers on the sills , the b pillar trim and the rear seat (easy) it's pretty obvious after that.