I have the older X-8N system with a bunch of GR-4 RX's, with that system, you have to toggle between HOTT and HOTTv2 depending on the type of Rx you are using... I don't know what the default setting is on the X-8E but I suspect this might be your issue. There is also a firmware update that is highly recommended by a couple other drivers in my area who are also running the X-8E. There is also another feature on the X-8N that asks you to enable the Tx when you turn it on, there is a light indicating that the Tx is sending a signal, probably worth making sure the same for the X-8E too.

As far as customer service goes, Graupner USA takes really good care of their customers. I'm sure they will get you sorted out by COB today.

Side note... I have several GR-4 Rx's in excellent condition that I'm selling for $20 ea