I agree with Swamp. Try both as stand alone units and see which sounds better.
I was a Nakamichi and NAD dealer and sold both of these units. The NAK should be a little sweeter, smoother and warmer in sound than the NAD, but the NAD will be a little more powerful and dynamic and have better bass control.
You'll just need to see which one is more to your liking and which has more synergy with the Pioneer speakers.
Let your ears decide.