You know what the caveat to this whole thing is? You can't exceed the maximum voltage of each amplifier. Since they're all connected in parallel, you can source three times the current but the rail voltage doesn't change. You'd have to find a very low impedance speaker to take advantage of the extra current. Having the current doesn't do any good if you experience voltage collapse.

The rail voltage of my Denon is about 35 volts. The A1400 on the other hand has a rail voltage of around 90V.

So why do they offer this then? Is it for low impedance speakers (like 2 Ohm) or is it so that you can double up on fronts?

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