This may be the wrong forum, but here goes. Can one use the widescreen mode and the P+S Technik Mini 35 Digital adapter on the XL2?

Yes, you sure can. Since there is no difference in the width of the image plane between the XL2 and other Mini-35 compatible cameras such as the XL1, XL1S, PD170, DVX100 etc. (all are 1/3rd-inch CCD camcorders), then there is no issue here.

Not only can you do it, but if you want 16:9 footage, the XL2 is probably far and away better than the other cameras. The other cameras that work with the mini35 don't have the ability to deliver full-res 16:9, so for widescreen 16:9 mini35 footage, the XL2 is the camera of choice.