The front 4x6's are tricky. Either you can get normal 4x6's like so:
http://www.crutchfield.com/S-SoN8uThogJK/c...search=infinity
Or you can get 4x6 plate speakers which give cleaner midrange:
http://www.crutchfield.com/S-SoN8uThogJK/c...search=infinity
Better yet, you can custom mount some 5.25 or 6.5 inchers easily in the doors, but I think you need an adaptor or something like that, but you'll get really nice results.
http://invision.aleromod.com/index.p...opic=531&st=20
Some people even get kick panels:
http://www.crutchfield.com/S-SoN8uThogJK/c...y=XL#morephotos