Anything that connects to your TV via HDMI should transmit it's audio to your TV via that same HDMI connection. At this point, since your goal is to use speakers external to your TV, which are connected to your amplifier, you need to connect your TV to your amplifier in the method denoted by your TV's ARC requirements.
If your amplifier can not meet the requirements for accepting the ARC from your TV, your only solution is to find and replace your current amp with one that does, or source your audio from something that doesn't require an ARC to pass audio from your TV.