Sounds like you've had it pretty good on the set up. I've tuned on a bow for weeks to get it dialed in right. As far as the twang, have you let someone else shoot the bow while you stand down range to see how it sounds from there? Here's how we do it. We set up a target near a big tree. The shooter is 20 yards from the target. The tree is about 10 yards from the target and about 10 yards to either side of the line of fire. You stand behind the tree while your buddy shoots the bow. Here you can tell exactly what the deer will hear. I've found alot of times a noise you're hearing while shooting can't be heard from the deers point of view.
As for the string leaches, they are as good if not better than any string silencer IMO. The limb savers are also money well spent. If you don't already have them buy some.
I shot my buddy's Q2 (not an XL) the other day. I did notice a little string noise while shooting it but down range all you could hear was the wind from the arrow.
Good Luck!!