Digital out problems

[Maureez Plays the Keez]

I bought 2nd hand Roland DM-20 monitors. They also have a s/pdif coaxial input and I tried to connect it that way to my Fantom X. I tried that with a normal cable (non coax) with RCA plugs. Result: no sound at all. Master volume is set btw. Do I have to buy a coax cable? (I expected at least to hear some bad sounds coming out if the signal was corrupted due to the use of a non-coax cable, but may be I'm totally wrong).
Or.. is it the clock rate (44.1Khz from the fantom and 96 Khz into the DM-20).

[Maureez Plays the Keez]

Closing this window I saw the DM20 .pdf manual and I looked right into it: Digital input select switch... it was on the optical side instead of on the coax side.

It sounds great btw, even with a non-coax cable
Not super monitors, but a lot of fun and clean sound for 120 euro's, and quite a lot of volume!