Before you do all of that, give Springer Precision a call. http://www.springerprecision.com/
If anyone knows what can and can not be done "correctly" on an XD platform, he will know. He is also a vendor on the board. http://www.brianenos.com/forums/index.php?showforum=160 I have spoken with him previously and have a couple of Springer parts in my XD.
I had no idea, tks. I'll talk at them. I'm not particularly set on the Sig I just thought the added blasty gases would work a comp real well and tame the beast. If I can get the same result from 9 or 40, that would be the smart choice.