It sounds like the Wadia will work with your Nakamichi. But my impressions of the Wadia are similar to those of Jab. My DAC is a Northstar M192, which has two digital coax inputs. My intention was to use the Wadia for music and my $170 Oppo 980H universal player for audio while watching DVDs. I am using the same digital cables for each source, Analysis Plus Digital Oval cables, and each source is plugged into the coaxial inputs on the Northstar.
Although I initially liked the Wadia well enough, at this point I have found to my surprise that I prefer music played through the Oppo rather than the Wadia. The Wadia is more convenient, but the sound quality is warm and fuzzy, and lacks a fair amount of detail. Supposedly, the digital signal out of the Wadia has a fair amount of jitter, which may explain my impression. Of course, you can always try to fix this issue with mods or reclocking devices (using a Monarchy DIP for $200 or an Empirical Audio Pace Car for $1800), but then you are starting to talk real money that might be put to better use with a transport. It all depends on how much you value convenience.