Why not just buy the companion Naim 5cdsi?
It is said to pair very well with the 5si amp. Plus Naim seems to recommend that you use the DIN connection over the RCA. The cdssi comes with the DIN cable in the box. The 5cdsi is a very nice player with an interesting way to load a cd, as you must open the cd tray manually and then apply a puck atop the cd. It seems to have a very good review in WhatHiFi and elsewhere. The Naims paired together should have great synergy. Yes, the 5cdsi is over budget, $1699, but you can grab one for about 10% off from Hawthorne if you call and ask for a deal. Remember, you are only buying it once, so it may be worth it. By the way, I own both the Naim 5si and the 5cdsi....
Lastly, I would be using Naim Nac A5 speaker cables with that Naim 5si...they will ensure that you are getting the very best from the 5si.