Are there any differences in the build materials among the (3) Montage options? For example, are they all metal housings and/or is the 7 or 8 more robust than the 6? I used to own the Tyros 4 (76) and it was completely plastic with a cardboard bottom (I know it's high grade but it's still made of wood). Once I repaired the EX7 and it had a AN1x toy-type keybed compared to the EX5. I know that the keybeds are the FSX on the Montage 6 & 7 and I also assume that they are all metal and built for hostile environments. I think the Motif 6 was also metal. The reason I ask is that I've decided to keep my beloved CP1 and just go with the Montage 6 instead of 8 but I don't want to lose any build quality either.