Don't know much about the tariff situation, but the you'll need to 'convert' the mains voltage as the US uses 110AC @ 60Hz and Europe 220AC @ 50Hz.
Then there's the problem that (heaven forbid) that it goes wrong, Roland US may not like working on a 'grey import'.

As to improving the sound, well all you can do is try..
I'm sure the XP and the XV will get alone fine together. You could use the XP in 'patch' mode (the effects tend to be more powerful this way), and let the XV do the work house stuff