What is not yet determined is whether some of the Android player apps that work with the Chromecast (including higher sample rates) are jittery or not? They might well be an alternative for some people without needing Roon. Android phone or tablet already in someone's possession would perhaps do the trick with the inexpensive CCA.
CCA's jiiter is a property of the CCA and not that of the source. CCA buffers the stream and the jitter is just a product of the crappy onboard Toslink transmitter it has. Sources may choose to compress the stream before sending it to the CCA which will lead to loss of fidelity as it happens with Chrome, this would be interesting to test, but this loss of fidelity is not jitter related.