Chord Dave - best input

To some extent. SPDIF IEC60958-1 defines a framing bitstream protocol for carrying multichannel audio. I believe the standard for consumer defines electrical properties and the use of 75 ohm coax as well as optical.
TOSLINK uses the same SPDIF framing protocol as electrical coax interface, but uses its specific TOSlink optical interface.
So typically SPDIF by default refers to electrical and TOSLINK to the optical equivalent, but yes they use the same protocols.

Thanks for the recommendation, mine arrived this morning and it does indeed play 24/192 with no isdues

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Other than originally the Toslink specification was only upto 48 kHz. There is no reason why better cables and interface couplers won’t support 192kHz (and I always say in hifi, better does need to always mean more expensive).
However I remember reading with Toslink the biggest bottleneck with Toslink are the interface couplers… ie what you plug your Toslink cable into. Many will max out at 96 kHz. DAVE will receive upto 192kHz stereo as it apparently uses higher bandwidth interface couplers

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That may be true Simon but the cable I was using before Sunday would not allow anything over 24/96 even with my Dave. The new cable works perfectly at 192

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Excellent.

A further comment on the opto-dx.

As I have understood it the reasoning goes that a dac that shows any minute detail tend to also show details from any remaining deficiency or disturbance. The scaler is a computer that does its thing (which is a completely different discussion). However, a computer tends to be noisy. While a number of measures are made, some RF noise appears to be present in the ground of the coax exiting the scaler.
In order to reduce this noise, suitable ferrites can be used (a lot of people seems to praise various cables having them).
In order to rather eliminate this noise, optical decoupling can be used. The opto-dx is simply an optical bridge having sufficient bandwidth for the two 0.7 MHz signals. Hence any noise present on the ground will not make it across, while the signal is preserved.

Using the optical toslink connection to the dac will also result in an electrical decoupling, but having a limited bandwidth.

In my setting (connecting the scaler with a tt2) I experienced dual coax (electrically connected, high bandwidth) to be comparable with toslink (electrically decoupled, limited bandwidth). Using ferrites on the dual coaxes improved things. Using the opto-dx improved things even more.

In order to venture further into the madness I power the two opto-dx units from different power supplies, this should result in even more electrical separation between the scaler and the dac. Have unfortunately lost count on how many cables and boxes that are currently used.

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