I would look in the direction of crons.
A cron is a file that lists tasks to run at some moment as batch commands.
For example, you can synchonize 2 website databases.
So, you could have your ’members’ site generate some cron and your public site being updated by the cron every 6 hours for example.
I don’t know how you can do this with MODx. Maybe with phpMyAdmin.
If you consider this solution, you should use search engines to find how to implement it.
Maybe someone else on the forum can further help.
thanks Jul! will investigate