If you're experiencing continuous failures updating firmware on a Tomahawk or Arrow-X receiver when using a Mac, try the following suggestions.
Try using a Windows PC instead. For fresh Windows installs of Paralinx Manager, additional steps detailed here may be required.
Try updating Radio 1 and Radio 2 separately instead of together if the update is getting stuck or failing right at the end of Radio 1.
Try the update in recovery mode. If doing a combined Radio 1 and Radio 2 update fails even in recovery mode, try updating only the Radio where the failure occurred (also using recovery mode).
Note: Recovery mode can be entered by turning the receiver on while holding the R2 button on the side. Release the button once the receiver has been powered on. The power switch can be used for this.