New TV: what to do with TOSLINK optical output

Your Cambridge 640A is a stereo analog integrated amp and has no DAC that’s the reason why it doesn’t have any optical digital input or any other digital inputs. Stereo analog integrated amps such as your Cambridge 640A only have analog audio inputs.

You will need to get a stereo integrated amp that has built-in DAC thus have digital audio inputs. Assuming that all your AV source devices have HDMI outs, if that’s the case and I imagine nowadays that all AV source devices would have HDMI outs, then you should consider getting the Cambridge AV receiver either the CXR120 or the CXR200. Cambridge Audio makes very good sounding av receivers and are priced reasonably. Then you can connect all your AV source devices using HDMI cables to the HDMI inputs on the Cambridge AV receiver. And you can use a single HDMI cable to connect the Cambridge AV receiver to your TV for video and OSD only. All AV receivers these days have at least one if not two HDMI output to connect to your tv display or a projector for video and OSD only. This would be the best way to set up.

EBay.
You can get a toslink and spdif to rca single ended output converter for about $8 shipped. If you are happy with your amp no need to waste money.
This little gizmo just needs a usb power source, just like a phone charger as it will come with a generic usb cable.

This will then convert your toslink to stereo rca which you just plug into back of your amp.

Been using one myself in the spare bedroom for same purpose for at least 3 years.

Problem solved.

Thanks for the input everyone, really appreciate it.
@tls49 its this tv https://www.amazon.com/LG-Electronics-OLED55C8PUA-55-Inch-Ultra/dp/B079TSV11D?psc=1&Subscription...
I found this guide for audio-out, looks like it is supported okay: https://www.lg.com/hk_en/support/product-help/CT20136005-1437129397190-others

@caphill, thanks for your lengthy reply! I have been avoiding HDMI switching since they are more expensive, I only have 2 speakers and only a small number of inputs to the tv (ps4 & laptop) . Is it better to use an AVR instead of taking the audio out of the tv? With an AVR, what happens to OTA signal audio?

A few votes for a small toslink to rca converter, seems like the easiest/cheapest way forward until I’m ready to upgrade the amp. I’ll start the coin jar for it now...

@mrgreenfur

If you’re only doing stereo then get a stereo integrated amp that has built-in DAC therefore will have various digital audio inputs such as USB, spdif (coax digital audio) & optical digital (Toslink).
The Hegel that you mentioned earlier will be a good option as long as it has DAC and thus will have various digital audio inputs. The Cambridge Audio also makes great affordable stereo integrated amps some models are analog only and have no DAC some models have built-in DAC so will have digital audio inputs. Rotel, NAD, Musical Fidelity also make affordable great sounding stereo integrated amps with built-in DAC so therefore will have various digital audio inputs.

And you can connect your PS4 using spdif (coax digital audio) cable or optical digital audio cable to one of these stereo integrated amps and let the DAC in one of these integrated amps do the digital-to-analog conversion.

You can connect your laptop using a USB cable to the PC USB DAC input port on the integrated amp.

Stereo integrated amps will sound better than AV receivers for stereo music playbacks. 

That's a lot of money to spend when $8 will fix the issue IF the OP is happy with his present receiver and sq from it.

Now obviously if the OP fancies an upgrade of receiver while they are at it then by all means...….