Mike there's a few ways you could do it.
Probably the simplest would be to buy the topping dac you mentioned then a chromecast audio. Link the two with an audio to spdif optical cable and Spotify will pick up up the CCA from within the app. For me that was the easiest and cheapest way to get Spotify through my system and it sounded good too.
Another way would be to buy a raspberry pi with a dac hat (hardware attached top) and have an all in one solution without the need for an external dac. Something from the likes of Allo give superb results for the money but there are others out there you could try.
There are numerous other ways but they are two I would go for.
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Current system:
RPi + Allo Digione
Beresford Caiman Seg & Dorado powered by 15v Linear PSU
Transcendent Sound Mini Beast OTL
Amptastic Mini-1
Klipsch KG4.5 Speakers with Titanium Diagphrams and Sonicap Cap upgrade
110aH Leisure Battery powers the Mini-1 & Digione