Nothing will happen to the power. if they claim 90 watts a channel, that's what will pas through the subs crossover and into your speakers. In most cases setting the sub through the receiver or through the sub's crossover doesn't make a difference, but if the receiver has a set crossover like the Marantz, you're better off going through the sub or you would be wasting the performance of your main speakers unless they only go down to about 100 hz.

-Joey