Yamaha RX-V479 turning off no warning

[MBBlat]

I’m using the above AV amp to pump out surround sound, source is an Apple TV box. With the resent warm weather is started turning off at random, unless the volume is set really low. Thinking it might be heat related I’ve taken it out of the stand to get some airflow, but this hasn’t made any difference.

I’m presuming something has failed on the amp, not sure if it’s even worth repairing or if I should just replace with something newer.

[MBBlat]

Any recommendations for a replacement?
I find I’m increasingly struggling with hearing the dialogue over the sound effects in modern movies and TV, do more modern amps boost the centre channel, or am I better off just getting a soundbar?

I already have a few old Sonos speakers around the place for music, is their soundbar worth it or just a gimmick?

Maximum budget around £500.