Just to update ... we went and bought some EnviroLitter, which is a pelleted pine-based litter.
It's awesome!! Our cats eyeballs almost popped out when he caught a whiff of it ... he promptly left. Later that day I checked the box and there was, uh, evidence of him being in there! Have seen both cats happily coming and going, so I think they are happy.
The farm house now has a lovely pine scent to it ... Also noticed that the kitties now have fresh, pine smelling toes