You are spot on with respect to relying on reviews, and my experience of Curry's in store advice is that they know less than I do in most technical stuff and I know next to nothing about things such as Sound Bars, my experience being limited to being able to spell 'Sound Bar' and that is even a struggle sometimes.
You're not wrong about Currys staff in the main. There are probably a few exceptions, but not many.
TV sound generally sucks. It has become progressively worse as TVs got thinner over the years. Sony's vibrating screen is a bit like NXT technology from the early aughties. It works pretty well, but is only available on their higher-end range, IIRC.
The frequency response of the Sharp sound bar at 50-100 Hz (+/- 6db) is a bit of a give away but is clearly referenced to the Bass Frequency Response and does not address the Treble and that should be in the 15kHz area.
I don't believe I referenced the whole sound bar as 50-100Hz, just the sub, and I gave the 60~100Hz figure quoted in their user manual specifications. The main sound bar frequency response is 200 Hz ~ 16kHz, but it +/-10dB, so a bit of a gap between the sub and the bar, and a lot of variation in the sound level across the range. Having said that, the in-room response of most loudspeakers is quite peaky too, so let's not lose any sleep over this.
The bar was bought for me as a present from my son, and Mrs H would not entertain expenditure in the £700 as a sound source, the TV was only £950 when on offer from Curry's reduced from £1700 so I consider I got an incredible bargain. The Sharp SOund Bar is an improvement on the In Built speaker, so in that respect it is a step forward.
Ah, things can be quite tricky when something is a present.
I had a look at the available sound settings on the TV and they are MPEG/Dolby Digital/Dolby Digital Plus/HE-ACC/Auto. In my ignorance I thought MPEG was a video format hence the MP(Moving Picture) reference, clearly I am wrong there. I am familiar with Dolby but have no idea what HE-ACC is all about, so in ignorance I left the sound setting in Auto, Your advice regarding settings and using Stereo PCM is not an option, so what would you suggest I use in that you recommend avoiding Auto.
It would be useful if you'd given the TV model number, then I could be sure of giving the exact info. As it is, my best guess is that you have the OLED55C1 (OLED55C14) model, but that's only a best guess. However, if it is that TV then PCM is an option, though I have to say that the menu choices are context sensitive. You do need to check certain settings before some options will appear.
I've composited three pages from the Web manual which replicates the TV's built-in help menus. The blue star and ring are my additions too.
There isn't an option for the TV to output HE-AAC in the menu list above. That CODEC only appears in the list of sound formats the TV will receive. It is converted internally by the TV to create DD or DD+ for the pass-thru setting, and converted to PCM if the TV is set to that mode.
HE-AAC is the audio CODEC used by broadcasters for digital TV and also used in streaming. It's a more efficient CODEC than the MPEG-1 audio formats used for digital TV. This goes hand-in-hand with the higher efficiency video CODEC used for HD and for 4K streaming.
Your TV and sound bar will be negotiating a common set of audio standards via the HDMI handshake each time the system starts up. It's possible then that the TV sees that the sound bar is only capable of stereo sound, and so the TV is automatically defaulting to PCM 2.0 out. You might want to disconnect the HDMI cable for ARC when the devices are powered off, then recheck the sound menus as if you were using optical. The TV can't detect an optical-out connected device, so whether something is plugged into the socket or not makes no difference to the TV. Run through the sound set-up menus as if your sound bar were to use optical and see if the PCM option appears. If it does, then set the TV to use it. Next, power down and reconnect HDMI. The sound setting should remain as PCM even if the menu option disappears. Double check that HDMI ARC audio out is working correctly.