Can you run the GM40 without a cab?

I'm not quite understanding this part in the manual, I know you can run it in silent mode WITH a cab connected, but nowhere does it say that you absolutely have to or do not have to have a cabinet connected.

I want to know if I can just bring my head to gigs and run it with no cab to use with in-ear monitors.

Yes, you have that correct, an external load is not needed.  Once the Power Soak is switched into (or has kicked itself into) silent mode it loads the amp correctly for it to be safe to use without any external load attached.  You can monitor it at that stage on headphones and run it to front of house via the Redbox XLR socket.

Thank you sir!