Lou, This perception that doubling your wattage will double your audio output is stiflingly bogus.
In my limited audio understanding, a two-way speaker, that has 100 watts available to it originally, would use about 12% of that power for the operation of the tweeter and about 88% for the operation of the woofers or potentially 12 watts and 88 watts, respectively.
When you biamp, since you attach one 100 watt amp to the HF and one 100 watt amp to the LF you then have 100 watts available to the tweeter, which does not need a power increase to operate. And you increase power available to the LF/woofers from 88 watts to 100 watts.
So, where you need the added headroom or increased power to the low frequency/ woofers you have now gone from about 88 watts available to 100 available which is about 14%.
This increase to your low frequency power causes an increase in output of about squat.
This is oversimplified and was not intended to be an audiologically sound explanation, but I hope it illustrates to you how biamping with your Denon doesn't double your available power or provide increased headroom where you might want it.