Xaro Xhoan Daxos and Lance Cav

If you use a token from Xaro Xhoan Daxos on a Lance Cav attacking you, to lower his rank by 1, how many dice will a charging Lance Cav roll?

Depends

It depends on how many ranks the Cav has, since you lower the ranks only for the normal attack rules, not for the Lance Ability.

So if the Cav has 2 ranks, it will roll 8 dice.

If the Cav has 1 rank (and you used Xaro token for literally nothing), it will roll 6 dice.