External DAC connection for Bluesound Node 2i (after "Another streaming newbie" thread)

Guys, just following recent topic raised by chuckccs, I found myself in similar situation because I was comparing Bluesound Node 2i sound via its analogue RCA output with its sound via external DAC (M2Tech Young DSD with external power supply). Difference was really marginal, especially taking into account additional cost of external gear (DAC, cable, PS). I connected Node to DAC via coaxial output, however not tried the optical connection. 
From those who got substantially better sound from Node 2i via external DAC I would like to ask which connection they used (coaxial or optical) and which cable they recommend, maybe also which DAC they used too. Thank you!