Just a heads up you can do this "double boxing" with the X1 and a secondary account. - i was note aware this was possible so in case anyone was wondering:
set up your x360 and create the xbl match on your main.
set up the x1, signed in with your main profile, switch profiles to your secondary, launch the game then search for the online match. Select the one hosted by your main from the results.
Complete the level (i used the first one) with your main, once completed, continue until the time runs out with the secondary. I periodically moved my secondary and sometimes completed sections of the race just in case it kicked an inactive player - this is one reason i always 'continued' (blindly) with the secondary after the race ended until the countdown timer finished.
For all my matches the second player did not cross the finish line.
you can combine this with:
select a pro boat - this will net you 1k at the results screen and combined with the 10 races needed for Taste My Wake this will unlock both.
you can also work on:
and you can just catch the buoy - if you see sparks after hitting it you are fine, you can also back track and loop around to hit it again if needed. For the final check point just bash into it - i did not hit the top number on this one and you do not have to tip them over.