I am going to buy Yamaha bbt 500 with 2x10 + 1x10. My question is, will it output 500watts at 2ohm, or 250 watts at 4ohm. It is 2 cabinets, both at 4 ohm. A friend told me that the amp is going to work in 500watts if I connect both cabinets to the amp. Instead of going 250watts with just one cab. Is he right?