The sensitivity difference is because the MAIN IN is expecting to be given the output of a preamp, but you’re plugging in a line level output - consumer, I presume, so -10 dBV nominal:
As such you’re over-amplifying the noise floor of the KEF sub output. Since you have a line level output, you just need to plug it into a line level input. Nobody is to blame per se, it’s just simple gain structure
Is there a particular reason you wanted to use the MAIN IN of the NAD amp? From what I can tell, that negates the use of the remote control as well as the front volume dial, which seems like you’re giving away a lot of convenience!
Thanks for clarifying but I think I am missing out on something here? Since I'm also using the preamp (pre-out) before going into the kc62, the volume control / remote is still controlling the overall volume and also the kc62 volume as well.
The you mean Tape in/Out - right? They are not controllable as I understand it.
If I would buy another Power Amp and just use the NAD for the Preamp, would that solve that? What would I have to look for that it would work out just fine?