I have pioneer 6.5" with these spacers in my bugeye without a problem
http://bit.ly/1glSVUp
There should be a few on eBay to choose from just search "wrx speaker" on eBay and they should come up.
You should get both front and rear aswell don't think I needed the space for the rear but Subaru have different screw layout than standard so the adapters help with that.