I have an Onkyo TX- NR535 av amp (under the stairs away from tv) it is connected to my Samsung tv, I have just connected my new Amazon fire tv cube to the tv but when I use the cube the sound comes out the tv and not the amp. I only have 1 hdmi cable buried in the wall to the amp, is there any other way around this please?
If the TV supports ARC then make sure that the AVR is connected to the HDMI-ARC port of the TV and turn ARC on in the TV menu. You may also need to turn the TV speakers off.
The receiver owners manual should tell you how to assign ARC to an input.
If the TV doesn't support ARC then you would have to connect the Cube to the AVR. You might be able to find a spot where it could still be voice controlled and require a shorter and easier to run HDMI cable than placing it at the TV.