Audio Note M6 - dark and thick sound ?

Hello All,
I recently bought an Audio Note M6 preamp and have paired it with a Nait 5i (set on unity gain). I hear a rather dark, thick and heavy presentation. The M6 is a very high gain preamp (18db) and when paired with 5i, the sound is too loud even at 7 o clock position on the volume control of M6. The sound at present is too full and overwhelming.

I dont know what exactly is the problem. I do not hear the dark thick sound when I listen to Audio Note gears at their showroom and of course Naim never has that darkness too. Is it a result of electronic mismatch that I am hearing this ? The input impedance of the Naim is supposed to be low, could that be the reason ? I am getting a bit impatient on this :-(