I have and ended up buying the JC1's. Both are very very good.
To describe the differences are tough but to my ear I found the Pass a little more "liquid" and the JC1's more detailed and dynamic. The difference's were not huge, especially with the JC1's in high bias mode.
Mono's worked better for my particular room and I would not be disappointed with either.
You really can't go wrong with either.
FYI mine are used with Aerial 10T's which love lots of power.