OK
Yep, it has issues.
Now tested with my old arena model.
Way to overcome them :
In export dialog settings in xsi:

The proof....(dx file playing)
(left click!)
http://uploads.savefile.com/redir/127605.zipOnly thing:
The exporter as 2 small errors...or it looks likes it to me..
First, here it's flipping VERTICALLY UV coords.That's never a problem with Ultimate Unwrap. U flip the UVs in Ultimate. U'll also need probably to do a "weld model" in UU, as often Ultimate Unwrap breakes per face when make an x import. That's common issue with x files and UU, anyway.
SO, do a weld model ONLY with vertices (not degenerate "faces") marked/checked in the "weld model" dialog box.
...Those are usual in any model conversion, and never are a problem, in engines I worked, flip the uv coords was easy, even, for the coder. But there was not a need. The worse is that...well..it seems to produce an small uv coords position (all at a time) offset...neither is a big problem: I just move the uv coords (select all previous!) with splitted window in UU, so I see seams are hidden. And in few seconds all matches perfect (otherwise, some seams are seen in texture limits)
I have done so, and output a correct file(b3d and x again), but also...well, some may not be using xsi for b3d, but for x based engines...hey, then do the old trick for these issues (I also tested to work perfect) : Just YET in XSI select all verts and flip the UVs in "texture editor" (quite a powerful uv editor, xsi has...as the 99% of the software, havent dedicate time to learn myself..) ...move em to compensate the export tiny offset(of course, no visual check, just calculate mentally what'll be needed). I happened to do perfect first time, as more or less had seen in UU in which direction the xsi exporter was producing it and visually how much...
I guess with some clever way u can even guess how much exactly, even numerically is offsetting in u, v or both...
And apply numerically before export... as a general rule...
U know what I mean.
Once done that(it's rather quick here), it's displaying ok in all my x viewers.
-do reproduce exactly those settings (exporting hidden objects may cause problems in some cases) .U see there's text format, matrix instead of usual rotate scale rotation...compress set to NO!. Triangulate unmarked (triangulate ur self previously , better) .
Plotting in XSI seems to be like baking in other tools...
that is, u want all baked. All as standard stuff, and the fewer "special" stuff from xsi, the better.
U have a full menu for plotting stuff somewhere in xsi, anyway, in xsi menus...btw, here I only needed just the exporter settings.
Here motion, curves... is being translated THE SAME, just like weights and all. :)
-Also, I made with "2d chain"s. I prefer NOT to use a 3d chains, nor a premade rig, but make my own with plain bones(2D chain! I don't like the others), weights, and use auto keyframing (well, I set a keyframed all bones initial pose) , and ...of course, I have a key asigned to toggle PIN OBJECT, at a joint(to plant foot, etc). One of the main things I like more in XSI.
Remember: I'm a noob. An xsi noob, I mean. I haven't read the manual (neither did in Blender and got the grips..I think ;) ) I just do quick guess to achieve what I need, as is my usual way.
Someone wiser with xsi(so, anyone) may see all this as absolutely dumb...
But is my way. XD
And actually, it shows it can do the stuff for b3d, x, etc.
The export once fixed as mentioned in UU, would be as trivial as usual is exporting an animated b3d file from UU.
I hope I have not forgot a thing.