I am going to say that the GPR will not fit crossroads bars, or the LSL risers.
If you look at the pics posted on the first page of the XBS, it looks like the top bar clamp is replaced. there is a cut out on the bottom right side I would assume to allow the arm not to hit the clamp in a full right turn. Also it looks like to stabilizer mounts to the top tree by two allen heads on either side which I would assume in into the middle of the clamp. So in other words you will have to use their top clamp in order to use the stabilizer. The crossroads replaces the stock top clamp, and the LSL's do as well. I just cant see how they would work.
Perhaps Puzzled or someone else can confirm this, I am only guessing by the pics posted.