I think that the most offroad tyre you are going to get in those sizes are Avon Distanzia, It's not a knobby, but it has a decent pattern for light gravel.
Having said that thou, I have an R1100S, and the smallest tire that oficcialy fits is a 170 rear, I asked the guy at my tyreshop, and they said that a 160 would work, but the handling would be diffrent, so I drove with one set of Distanzias on it.
Since the tyre was to small the profile turned out to flat, but that worked quite well when I was driving gravel and light mud with the S, it became more stabile which is good when it's sliding. The onroad performance was however also affected, and it lost allot of it's sportiness, so I'm back on sport-touring tyres now.
I would think that a rear 150 TCK would work (however it would be to flat), but do talk it over with someone in a tyreshop before trying. I have no idea about what sizes the front comes in, so that might not work with the TCK.
You could have a look at Heidenau K60 to, but I don't know what sizes they come in other then GS sizes and offroad sizes.
I have read about people putting rear ofroad tyres on the front rim, but I don't know if there are any good ones that fit.