Thanks, guys! I am thinking that I will go with the SIG brace first, and will figure out if I can find a foldable or adjustable stock to add to the trust.
I waited a while to get a conversion kit for the P320, haven't seen any parts available for the 556xi, so I am not counting on finding whyptmi am looking for anytime soon.
Thankfully, my order for additional magazines is still open with Cabela's, and I am still awaiting a call from them to come pick 'em up.