I have none of those watches or bracelets. However, I think taking the bracelet
from the smaller case to the larger case might fit with no trouble. I think a critical
factor is the lug length. I don't have photos to compare the lugs. The Sinn 917
shares the 44mm case diameter, but the case is much thicker. I would try the
6090 bracelet first.
Here is my suggestion. Call Sinn sales rather than customer service. They have
demo models in the show room. Ask them to take the bracelet off the 6090 and
put it on the 6100. When they are successful place the order.
Some may say, the case sizes are different. How could that work? Well, here is an
example two different case sizes on opposite ends of the same bracelet.
Thanks,
rationaltime