overdubs out of time

ok this has become very bothersome, my partner and i are having sync problems between our two PCs. We record rhythm tracks off a line 6 mixer which records individual tracks as 48/24 waves which imports nicely into cubase 8.5. Everything lines up perfectly. i then either send a mix done in cubase or the individual waves and he then puts them in audition or cool edit and does overdubs also in 48/24. when he sends the overdub files back to me and i import them into cubase they are out of time, no matter if they were recorded from the beginning or started somewhere in the track. If i put them in cubase at the exact time they are listed in audition or cooledit they are still out of whack. This started when he got a new PC. Any ideas cause i am goin batty having to aline tracks by ear and or eye. thanx