Instead of an integrated, why not buy a Mac Power amp and scrap the Rotel. Big difference. That way you can keep using all of the features of the Marantz.
For the wattage, 100 watts to 200 is only 3 db. Also, I would guess that the Mac's dynamic headroom will make up some of this difference. Look at the weight and size of the power supplies. There are plenty of 20 watt amps that sound better than less expensive 200 watt amps. Go look at the specs of a Pass Labs or Jeff Rowland.
For the wattage, 100 watts to 200 is only 3 db. Also, I would guess that the Mac's dynamic headroom will make up some of this difference. Look at the weight and size of the power supplies. There are plenty of 20 watt amps that sound better than less expensive 200 watt amps. Go look at the specs of a Pass Labs or Jeff Rowland.