He's using a Helix though, not a tube amp. The question at this point is why he's using a Power Station at all when the Helix should take care of all the poweramp and cab simulations itself.
Hey man, I'm on your side here, but you are going to blow something up if you're not careful.
For one, why are you using a Power Station with the Helix at all? A Power Station is a device specifically made to take tube amps and bring their output safely down to line level while preserving its tone. But you've got a Helix. It already outputs a signal at line level. What you want to do is plug your Helix output directly into your mixer. Don't even bother using the Power Station unless you have a real tube amp to use with it.
Also, the reason you're getting no sound from the Power Station is probably this, from the Power Station's manual:
"IMPORTANT: The SPEAKER 1 jack has an open load protection feature. If no cable is connected
to this jack the Power Station will remain locked in BYPASS/STANDBY mode regardless of the
front panel Standby switch setting. This is done to prevent potential damage to your valuable
vintage amp should the speaker cable become disconnected while in Bypass mode."
And another warning... If you plug a cable into the Power Station's speaker output jack with no guitar cabinet plugged into the other side, you'll blow up the Power Station's tube power section.