Actually the RR-2150 does have a digital input; the USB on the back panel. I'm not all that versed in the variety of iPod accessories but is there one with a digital out via USB? If you are looking for a DAC I can recommend the Cambridge Audio DACMagic. I use it to feed digital inputs from my CD player, Airport Express and laptop to my vintage integrated amp with great success. Enjoy!
_________________________
AvFan
Outlaw 976 | ATI 2005 | M&K 850s Left, Center & Right, Surround-55s, MX-70B Sub | Harmony 950 remote | Panamax 5100 | OPPO UDP-203 | LG OLED55B7