Run each pair in series to one channel and the two of them will be at 8 Ohms. Your NAD can handle that. If you just run them A & B (parallel) the load would be 2 Ohms which might give your NAD fits. I've seen claims that the NAD 3225PE can handle 2 Ohm loads, but I would be careful if trying it. It could run very hot and cut out or blow a fuse if it doesn't like it.

To connect in series run the positive lead from the amp to the positive lead of the first speaker, then run run the negative lead from the first speaker to the positive lead of the second speaker, and then run the negative lead from the second speaker back to the negative lead of the amp.

You could try stacking them with the top speaker upside down which might surprise you compared to them individually.