Joe,

That really is a beautiful piece of work.

The combined load of three in parallel like you suggested would be about 3 Ohms. I very much doubt the Denon would have a problem and if it does, it should gracefully shut down the centre channel. If you plan on trying this, start with a lower volume and gradually increase it. Let us know what you find out please.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated