What is the benefit of a second amplifier .

I’m still trying to decide what direction to take. Play all my speakers through my B & K 200.7 amplifier or have the main speakers run by a Second dedicated 2 channel amplifier. I’m trying to get the best sound possible from my main speakers, B & W 803s. When listing to 2 channel music I want to hear all the detail, and everything the speaker has to offer. When watching theater I want the full effect of the movie. I spoke with a gentleman from Morantz, who said I would gain nothing with the second amplifier and all speakers should go through a 7 channel amplifier and processor. I could then just hit the 2 channel button for analog. He also said in 2 channel analog the 200 watts are dedicated to my main speakers. I should hear everything I want to hear, there must be some other problem. The 200 watts would only allow me to listen to the music louder. There is no need for a second amplifier. If you say the second amplifier is better how do I hook this up? Please explain why it’s better. When watching theater all speakers should work together. When listing to 2 channels all speakers are off except the mains. I don’t want to move speaker wire between two ampfliers.