Yeah, as long as the same tires are on the same axle, you should be
okay. The quattro IV system - which you have - is okay with different
tread depths that way. You should have similar tread depths on tires on
the same axle, though. On some of the older systems they recommended
that you replace tires in sets of 4....
'04 A4 1.8Tq MT-6
Central NJ USA