aliahk:I have a nait 5i myself and it has no digital out so I think it wont make any sense.
Am I right?
I think you have missed the point of using a DAC.
It makes perfect sense to use an external DAC with a Nait 5i (or with any amplifier).
Feed the DAC with digital output from sources like computers, PS3s, BluRay/DVD players/recorders, Skyboxes (or whatever) and it converts the digital signal to analogue which plugs into your Nait with RCA phono like any other normal source like a CD or tuner.
I have used a DAC with my Nait 5i since the day I bought it.
I think the rDac with a Nait 5i should be an excellent combination.