This past fall I potted its buddy up in Lance Birk's "pretty good mix" which is a basic bark mix with a portion of coarse sand in it. A lot of my barbatas have been switched into this mix with pretty good looking roots developing (using clear aircone pots). The tigrinum in this mix is making lots of new roots, but it's always been the better root producing plant of the pair.
The sand doesn't seem to be that much of a modification. I thought it would wash out pretty fast, but it stays in just fine.I have been wondering about that mix. It just seems counter intuitive.