You could definitely give the benefiber a whirl. I tried it when I ran out of the acacia and it didn't give me problems. However it is gritter than than the acacia and call me a tree hugging hippy but the the acacia being organic appeals to me. Obviously you'll still have to build up slowly with the benefiber.
On the other fiber supplement choices give a miss to anything containing psyllium or inulin. Also the sugar free varities contain sweeteners which can cause IBS symptoms as can the flavored varieties.