Ok, I did the comparison.
I have compared Chromecast Audio with Toslink, MicroRendu and USB direct from Nucleus into a Hugo 2.
I listened with headphones, the Audeze LCD-4z.
I found no differences with 96k content or with 44k content.
In fact, when using the remote to switch source on the Hugo, it switched instantaneously when going to USB (took about a second to lock onto optical), and once I had the album synced well enough that I heard no interruption or change, I had to check the color of the indicator light on the Hugo to see that I did in fact switch.
That is impressive with a $35 device.
One caveat: I did notice a bit of harshness on an EST track — the piano is a bit harsh and jangly on the beginning of Dodge the Dodo, obviously intentional because it is perfectly smooth at other points in the track, but I thought the CC made it extra harsh. Which might indicate that it has trouble with the complex high frequency tones of an abused piano. I could investigate more. And I never noticed it elsewhere.
But note that I did hear differences yesterday with the Bel Canto DAC 3, which is a fairly old device (about 2010, I guess). So this supports my standard theory that the importance of the quality of a producer depends on the sensitivity of the consumer, and the Hugo 2 is very new and brilliant.
I should also mention that I used the CC with the ugreen adapter for wired connection. Yesterday I tried both wired and wireless, but today when I moved it to another room, it didn’t work at all. Wasn’t visible in Roon or the Google Home app. I finally managed to get wired working, but not WiFi. Setup is infuriating. You go through the setup, initiating with Bluetooth and then provide WiFi credentials, it finally shows this screen; you notice the absence of any suggestions and of buttons to do something. This is the entire screen on my iPad!
Hit the X in the corner and it says Setup is not completed, Resume or Exit. But there is no way to Resume. Both the app and the documentation are written on the assumption that you are an idiot, beautiful when things go well, but hopeless when they do not. Took a long time to get it working yesterday, I thought I was done, but had to start over today, took equally long.
(The three dots in the upper right include Help, which was useless, and Feedback, which I provided, forcefully.)