It drives the majority of headphones. Which is why I continue to love my iQube, but it does have a little trouble with higher impedance cans like the AKG 701's and HD650s (nearly have to max out the volume
on the higher gain setting). Probably a trade-off for the amazing battery efficiency.
I use my iQube all the time with my Denon D7000's, so it should be good with your D5000's too.