300 will be a little shy of what you need to really do horns correctly IMO. I really don't see how the Focals will get you what you want either. Just putting them into factory locations won't really give you any significany (if any) improvement on your current setup in the areas of staging and imaging.'

You may be able to build a set of kickpanels that integrated a dead pedal. Otherwise, your best bet will probably be to save your money, wait until you can get a second amp and then try the horns. Either that, or try to find some one selling the CD1Ve Horn comp set with the midbasses and crossovers.