Canon 881 - §1. The Christian faithful are bound by the obligation to participate on Sundays and feast days in the Divine Liturgy, or according to the prescriptions or legitimate customs of their own Church sui iuris, in the celebration of the divine praises.

§2. In order for the Christian faithful to fulfill this obligation more easily, the available time runs from the evening of the vigil until the end of the Sunday or feast day.

§3. The Christian faithful are strongly recommended to receive the Divine Eucharist on these days and indeed more frequently, even daily.

§4. The Christian faithful should abstain from those labors or business matters which impede the worship to be rendered to God, the joy which is proper to the Lord's day, or to the proper relaxation of mind and body.

Those are the relevant canons from the CCEO. To me, they seem to say that this is not actually permissable. However, in my experience as an outsider looking in, many Eastern Catholics are content to ignore them, and instead listen to their bishops and priests, who tell them it is permissable for them to attend Orthodox services in lieu of Catholic ones.

And really, the CCEO itself is a massive Latinization imposed by Rome.