Actually it's the other way round, the original can dissipate a surprising amount of power, see fig 1 here:
http://www.meridian-audio.info/public/quad_405_test_reports[2314].pdf
The 1/3rd power both channels driven is a VERY stiff test,
Astonishingly thorough review!!!!
However, the 405 was not designed to drive 4 Ohm loads - see the power output tests. Not sure how much more power the Mk2 coud manage into 4 Ohms.
It would be interesting to know what NetAudio has done to the design. But removing the protection features (if they have done) is very risky with one pair of output transistors and 50V rails... as has been argued (both ways!) in the DIY pages.