Hi Richard,
Like Caerus I initially used a Yammy HT receiver (1600) to drive my Logans. In my experience the pre-amp makes a much bigger difference than the power amp.
My own observations may not apply to your Marantz. When I replaced the power amp part of my Yammy with a pair of mono blocks the sound quality did improve. But only when the Yammy pre-amp part was replaced by a decent line stage did the sound quality improve in leaps and bounds! Watts alone don't matter. Recently I replaced the power amp part of my Yammy with a separate multi-channel receiver. The sound is still the same. But, the new amp hardly gets warm, while the Yammy is cooking!