I posted in your other thread yesterday and I just came across this one. I can add a couple of things. Aside from using 2 preamps, which can't be a good thing, Naim is one of those brands that insist you use one of their preamps with their amps. Spectral is well known for this as well. I think its absolutely necessary you try your preamp with something else, just because of that. You will be able to gain some info on how your preamp really sounds. Using it with the Naim is no way to judge it.
I know a dealer, Wellington Audio in FL, that specializes in UK gear. He has both Naim and AN, and most, if not all of their complete product lines on display. Those are his 2 main brands. Depending on where you are, I don't know if he can sell to you, but he may be able to help. Last time I was there, I saw your Nait and the M6 in the same room.