Ample choice for Toslink endpoints: in Pi HAT-land, apart from the Hifiberries, there’s the Pi-Digi+ from IQAudio, the Digi HAT from JustBoom and the 502DAC - Pro Audio Shield from Pi2Design to consider.
If you fancy something other than a Pi, an Odroid C2 with a Hifi Shield is a great option.
The Cubox’s optical out is OK, but not great (yes, @Sloop_John_B – you were right ;-)) – I would not buy a Cubox for this (USB is a different story).
The Bluesound Node 2 sounds great, is RoonReady out of the box and a true Swiss army knife for audio. Not to mention the best fun / greatest convenience I’ve ever had from an audio endpoint.
From Auralic, there’s the Aries mini and Aries to consider. Alternatively, the Mutec MC3+USB is a very well-clocked, low jitter USB device with a plethora of options and outputs, including optical.
By no means exhaustive – just adding a few good options to the mix. 