I don't have a Motif, but I was able to connect my MODX synth to my Tyros 3 and play the MODX through the Tyros 3 speakers. You would need two 1/4"-jack audio cables to connect the Line Outs from the Motif into the Line Ins on the Tyros.
Also, I'm not sure about whether the Motif XS had "balanced" outputs. This may affect what type of cable you need. As far as I know, Tyros 5 doesn't have "balanced" outputs.
Hope this helps!