There are very few headphones that are going to take advantage of all the power that the Kaiju has to offer. Having said that, if you use the DC filament upgrade and wire the outputs for 2 Ohms, yes, you can use the Kaiju as a headphone amplifier, though you'll also need a preamp.
If you aren't powering K-1000's, HE-6's, or a similar pair of headphones, I would take a more serious look at the Mainline.
-PB