Hi, and welcome
First thought, why do you want a new Amp? What problem are you trying to solve?
The NAD is good and if, as you say, it's loud enough and you don't hear noise in the quiet passages of music... then changing the Amp is very unlikely to make a difference.
Fair enough if you just fancy a change, it's your system.
The PA7 is very good, if you decide to go there.
The biggest impact on your sound is your speakers *in your room*
Have you used the WiiM room correction, how do you find it?
Perhaps start looking at new speakers?
Probably even better, just enjoy the music