I would definitely try through the ESC first, because you’ll definitely be getting safe voltage. Assuming you have your ESC, plug the servo style wire from the ESC into channel 3 on the receiver and then plug the ESC into the battery.
I probably wouldn’t plug that 2s battery in. It seems like your receiver could handle it, because it says up to 8.4v, but I think it passes the voltage straight through to the servos, and I’m not sure that they could take it. That would be a good battery to hook up through the ESC though.
One last thing, it’s possible that you have the receiver set up for PPM instead of PWM, and then the servos wouldn’t work. I believe that setting is in the left main menu, under Rx something or other. It’s PWM by default, so this would only apply if you had changed that setting.