Not so fast - if your Vi is HARDWARE VERSION 805 and you have updated the to FIRMWARE VERSION 15 you should have no problems.
BUT (and I know this from personal experience), if your Vi is HARDWARE 705 it will not update to FIRMWARE 15 - when attempted it says UPDATE NOT NECESSARY. BUT (and this is the BIG but) it will NOT work properly on the DSiXL. It will load properly but every game I have tested - and many others that other users have tested - will freeze up within a few minutes. There does not seem to be any rhime or reason for the amount of time it takes to freeze, though older titles seem to last a bit longer.
The EZFlash guys are working on an update to firmware 15 that will work on the 705 hardware, but it is not available yet.
Steve