muzikman, it's not necessarily about integrating with the MODX schema. You can create your own schema, create and load your own object classes, and use xPDO to interact with the DB.
In your case, I don't think you'd want to carry the overhead of a resource (or other MODX object) for each movie at your site. You could create tables as you've pictured them, use xPDO for the DB layer, and write your own CRUD code with xPDO.
If would be very handy to be able to use xPDO methods like getObject(), getOne(), and getMany() with your DB and do xPDO queries on it, but you don't need to subclass any MODX objects to do that. There's some info here on using custom tables:
http://bobsguides.com/custom-db-tables.html. The method there won't work for you because you have many-to-many relationships, but it might give you some ideas and the links at the bottom of the page are useful.
The only advantage of piggy-backing on the MODX schema is if you want to use existing MODX extras like getResources to display results, and I don't think you need that.
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PLEASE, PLEASE specify the version of MODX you are using.
MODX info for everyone:
http://bobsguides.com/modx.html