oooops.....
forgive my ignorance....
just referred to my wife's Denali owners book, and looking over the set up....
I think they are actually fog lights not driving lights (though would certainly put out more light than the H2's)and are wired into the headlight relay and actually turn off when hi beams are selected.
I will take a look at the vehicle tonight and measure bulbs etc. to see if it might even be possible/feasable.