Diki:

I have a Tyros 3 and a Motif XF and have the same problem. I create a performance with multiple variations on the Motif and then select a Style on the T3 with several channels muted. This gives me a lot of flexibility. However as you noted when I change variations I have to quickly hit buttons on both keyboards and sometimes, more than I like, the two are out of sync by a beat or two. So even with two Yamaha boards this is a problem. Not sure if would be a problem with two Arranger keyboards of the same manufacture but that is less likely scenario in any case.