I've got an Alpine 3553 running 6 gauge wire, and a RF 700.s on 4 gauge (seperate wires) in an otherwise stone stock Camry... No big three, Regular ol Die Hard batt... No dimming, and no other problems of note...
Exact same setup in 2 different (2000, and 2006) GMC trucks, and no problems there either...
Admittedly, its nothing massive, but hey...