You are right... there is no USB host port like the SHD. Thank you!!
I think I have three options and I have not made my mind yet... the context is that I will play musing on my Flex using a PC (either USB or Bluetooth).
1) The amp is powered in tandem with my PC. I can connect the amp's trigger input to a PC's USB port. The bios needs to be setup so that USB ports are turned off when PC is turned off. An alternative would be to connect a 12v trigger cable to a MOLEX cable directly attached to the power supply (this requires slicing the cables).
2) Use a smart power bar like the link I provided above. The Flex's power is connected to the "control outlet" and the power amp's power cable is connected to one of the "automatically switched outlet". The power of the Flex and amp will be perfectly synchronised
3) Use a more standard power bar that can be turned on/off with a remote. Connect the power amp to Emotiva's ET-3 Trigger Expansion Module. Connect the module and the Flex to the power bar.
https://emotiva.com/collections/accessories/products/et-3