Cathay Pacific in Hong Kong fly A340 and A330 - MFF.
The CCQ (Cross crew Qualification) works by the pilot being fully endorsed on one type. After a certain period of experience on this first type (say 200 hours), they are enabled to do a day course on "Differences" and a training sim. This is followed by the regulatory sims then some line training.
A line check is followed by a minimum number of sectors on only the new type (say 10), then they are fully qualified to fly both types.
To keep legally current on both types, a pilot must do at least 3 T/O's & LDG's in 90 days, one of which must be on the other type.
Each concurrent annual line check must be on the other type than the previous one.
Each 6 months the regulatory sims (Instrument Rating, Aircraft Rating and IAL) must be done on the other type than the type checked on the previous one.
I hope this info helps.