I did follow the manual and set the Pedal/Ext Amp outs from Exp ins to Amps. Created an Ext Amp block on both momentary and latching, tried all tip + ring combos, and still no change on the amp. I've scoured a bunch of reddit forums and no confirmation that this indeed works.
I could only confirm that the RJM Amp Gizmo with the correct cable can achieve this which someone in an EVH facebook group was able to confirm. No confirmations yet on the HX Effects as far as I can tell.