Yes the sensor is moving..
I created a new model in the DS16. Set everything up with a second iGyro and an expander, together with the two REX3's. Now everything worked!!
Back to the original model, cleared the Dual Path. Set it up again, now with the two REX3's, paired the DS16 once more. Now the original model worked as it is supposed to!
I have NO idea why it originally didn't work, I had not used any other RX'es prior to the REX3's. so the pairing should have been correct. Nevertheless, starting from square one, no configuration changes, just a re-pairing after removing the Rsat2's solved it.
Thank you for your quick response, always appreciated your service!