Audiosu, the output stage inside the Denon is a version of my own preamp output stage. :-) This one is Single Ended.
The NWO-2.5 tube stage is differential (balanced) which, among other benefits, results in significantly increased output power and much lower output impedance, so it is considerably better than the one in the APL 3910. :-)
When it comes to NWO-2.5 and a preamp is like having two of your favorite SOTA preamps hooked up in series. Of course, one preamp would sound better than two in series making one of them redundant. :-)
Regards,
Alex