Even at what you would think as extreme volume levels, I would be very surprised to measure more than about 100 watts or so being delivered to your Polks. Speakers nowdays are far more efficient than they were in the days of stereo-only reproduction where it would not be unusual for a speaker to consume 200-300 watts on peaks, especially with music that contains a lot of bass.

Believe me, you are not going to need anywhere near 400 watts with your Polks unless you don't care about blowing them up, or are deaf, or both.