A ULE body won't turn a standard mag into a X-Mag. It'll give you an aluminium vert-feed body which is threaded for 'cocker barrels and uses Angel ball-detents.
The closest you can get to a X-Mag (without actually buying a X) is an E-Mag with X-valve and all ULE parts (ULE body, ULE rail, ULE frame). That gives you a marker which is functionally identical to a X-Mag except for the ommission of ACE. That's the route I went with
mine.
Level10 rendered ACE a bit redundant in the anti-chop stakes, however it does still offer some benefits with the newer software's shot buffering and is a 'belt n braces' approach to preventing chops.
You can buy a 'proper' X-Mag upgrade kit (a complete X-Mag body) from AGD-Europe, which will replace the body and rail on any mag (except the original RT). However they're more expensive than the ULE (about £40 more for a non-C&C, £180 more(!) for a C&C) and they don't look good on non-E-Mags, as you get an overhang where the battery should go.
If you've got an E-Mag you can go the whole hog and get a X-Mag upgrade kit including both the body and the ACE, but you're looking at BIG money (£400 for a C&C) for naff-all performance gain.
Like L1f3 said, the 'box' is the battery for the mag - they don't need external secondary regs in the same way that cockers/Angels etc do - as the mag valve has a reg built into it.
