Naim grey I/C, is DIN to RCA different from RCA to DIN ?

You can use the same cable but it is "directional" - i.e. it's mean't to sound better one way than the other - so you'll be running it backwards, and it may not sound quite as good (plenty of threads here on the whole subject of directionality in cabling).  My own view is that for relatively non-critical situations then running a cable the wrong way is better than not being able to run any cable at all...

Thank you Richard for your reply. My doubt was referred to some ground problem due to the fact that I have to connect the cable backward but I do not know what is the internal cables difference between DIN-->RCA or RCA-->DIN. 

Your best bet is that if you're in a pinch, try it out and see.  I'm pretty sure the wiring is the same, it's just the 'directionality' of the cable that's different.

Thank you Richard, I was afraid that the different internal wiring may damage something but probably not because the wiring is the same and only the directional is different. I'll try it during the week.