MA352 into Power Guard

I recently bought a McIntosh MA352 integrated amp. It's teamed together with Monitor Audio Silver 500's and a Rega Jupiter. The system is set-up in a dedicated 300 sq' music room. I typically don't drive the amp much past 30% on the digital readout but the other day I was showing it off to a friend and ramped it up to 49%. During a rock CD playback, the lights under the tubes flashed for a second from green to orange indicating the built in Power Guard was activated. This happened twice before I got to the remote to lower the output. I understand what occurred. My question here is why? The MA Silvers are 8Ω  and rated up to 250W. The MA352 is 200W. I'm not an electrical engineer but a life long audiophile and I understand enough to assume all the parts here are within compatible range. However, I don't understand why I can't drive this amp further without the PG feature kicking in to prevent clipping. Any thoughts as to what's going on are appreciated.