@AndyHutch
HDMI Device Type should be set to AV Amplifier. Set the Number of Channels to 5.1 ch.
Audio Format (Priority) should be set to Linear PCM for gaming or when watching a DTS-encoded Blu-ray disc. If you prefer lossy DTS Digital Surround audio from DTS discs, change this setting to DTS.
When streaming content from the PS5 or watching a Dolby TrueHD/Dolby Atmos encoded Blu-ray disc, change this setting to Dolby.
When watching Blu-ray discs, there is another audio setting that must be adjusted when you start the disc. Tap the Options button on the controller, select the “…” and change the Audio Format setting to Bitstream for Dolby-encoded discs. Change this setting to Linear PCM for Multichannel PCM audio from DTS-encoded discs. Change this setting to Bitstream for DTS Digital Surround audio from DTS-encoded discs.