The SR-18 is an older surround sound receiver than the SR-8500. Both are discontinued products from Marantz. The SR-18 specs claim this unit puts out 140 watts RMS from all 5 channels into 8 ohms. The SR-8500 is rated at 125 watts x 7 channels into 8 ohms. But be careful with the later Marantz models. I had a conversation with them directly recently. It seems on their current line of 7 channel A-V receivers, the stated power rating are for two channels driven. When all 7 channels are driven, they guarantee only 70% of the stated power rating in watts into 8 ohms.
When evaluating any new A-V receivers, be sure the specs states "all channels driven" at the same time.
When evaluating any new A-V receivers, be sure the specs states "all channels driven" at the same time.