I have re-read the operating instructions, and they don't specify a power rating into 4 ohms. They do say that the amp is designed for 4 and 8 ohm loads (basically, any load not dropping below 2 ohms). FWIW, before I bought the amp in September, I spoke with Frank Van Alstine, and was he was quite confident that the amp would easily drive my Magneplanar MG-II B speakers.