Screens come standard with the set, but they're the smallish ones that don't block much of a wind. Pretty sure standard size clips also come with the set, but those wouldn't necessarily be ideal for XY. You'd need a riser or shim or whatever you wanna call it between the clip and your t-bar.
If XY is your thing, I'll be honest with you that the STH-100 mount is really perfect for that. It puts the capsules in a really TIGHT XY position relative to each other. Plus the mount allows you to vary the included angle.
The problem is the figgin' mount is absolutely ridiculously priced...totally not worth what Neumann charges. However, since I have the mount in my bag, I actually like it quite alot. I'd say that you get what you pay for and I suppose I could suggest that you'd be happy with the mount, but in this case there just ain't no way the mount is worth anything close to the $300 Neumann charges for a new one.