The relay you are speaking about is way up inside of the driver's footwell. I have not been able to get to it, but simply bypassed it through the elimination of the factory speakers. I went with a set of Infinity units and they sound amazing in the back. For the fronts, I used a set of 6.5" Bose units from a 2005 G35 Sport and they sound like crap. Just get a nice aftermarket set and you will be more than pleased with the results.
The front speakers are only 4" units that are extremely weak. I just took out the whole box/amp unit, created a template from 1/4" oak plywood, and installed the speakers from there.
NOTE: Any speakers you add to the front need to be shallow mount in order to clear the window track and window behind the speaker. Just trying to save you some
