Currently I have and am using an ampeg b2r head (not the newer b2re head). It's rated at 350 watts at 4 ohms and 200 watts at 8 ohms. I am using it plugged into one 4 x10 cabinet which is the ampeg b410hlf. That cabinet is rated at 400 watts at 4 ohms. First question. Am I currently running my head at 8 ohms or 4 ohms? Due to head/cabinet mismatch, is it a problem to continue running my set up this way? Second question. I want to add an 1x15 to my stack for larger venues. Can I add an 8 ohm ampeg 1x15 cabinet to my current setup without blowing things up? If not, assuming I want to keep my existing head and still run a 4x10 and a 1x15, do they need to both be 8 ohm cabinets? Thanks!