Here's a summary of my opinions on the amps I have.
The Hp-p1 is probably the only amp I own that I actually like the D5000 on. My D5000 aren't balanced so I can't use them with the Mjolnir. The D7100 also do well off the Hp-p1 and sound great off the Mjolnir so I suspect the Mjolnir might be a good amp for the D5000 as well but no guarantee as my next opinion shows.
I don't really like the D5000 with the Apex Peak although I do like the Peak with the D7100 so go figure.
I also have an Objective 2 which is a good $150 amp but I find it unpleasant to listen to as it's pretty unrefined. I keep trying it with my Hp-p1 as the DAC and always switch back to the internal amp on the Hp-p1 after about 5 minutes. The Objective 2 isn't terrible but the internal amp on the Hp-p1 is much smoother sounding, more musical and far more revealing. The Objective 2 does seem to keep the Denon bass fairly tight although with the D7100 there is more bass than any other amp I have which makes them sound like a bass heavy headphone which is not really how they sound on better amps.