RCA outputs to COAX input - is there only a splitter or is a extra device needed


RCA outputs to COAX input - is there only a splitter or is a extra device needed please? My BLUESOUND VAULT only has RCA outputs and if I use it as only a streamer and de ide to get an external DAC such as Musical PARADISE Tube DAC or a Denafrips DAC I will need to connect to COAX. Also these DACs seem hard to find. 
Thank you,
Agentwja 
agentwja
The Vault has optical toslink output use that. 

Audio

Analog RCA stereo jack, TOSLINK digital optical output


Get a quality build multi-strand real glass fibre toslink cable, and bypass the cheap crap plastic ones. The audio quality step up is big and top-shelf. 

I have bought two brands that I use: WIRE-WORLD TOSLINK SUPER NOVA 7 and DH Labs GLASS MASTER TOSLINk

Both are good, but in my bake-offs, the more expensive WIREWORLD was a step-up
https://6moons.com/audioreviews2/wireworld/2.html