I've been using an RPi with an outboard EarMen USB dac, and with a HAT dac, for more than two years and I liked the sound pretty much, but the Volumio quirks, instability and sensitivity to different usage scenarios were just too much for me.
Last year I've got a WiiM Mini, just to try it out, and it was a very pleasant surprise - on it's own, it really isn't something to write home about, but with a decent outboard dac, the sound quality is comparable to the RPi's (in my opinion and in my system).
Finally, I've decided to let the RPi go and cancelled my Volumio subscription, in favour of my WiiM Mini. I don't regret the decision at all. As well, I don't regret not buying a WiiM PRO - it's practically the same thing as the Mini, just with a bit more inputs/outputs. In my opinion, the omission of a USB output on the PRO is a very big missed opportunity - with a USB, it could easily compete with the NODE, but without the USB, there's no point in buying a PRO. Just buy a Mini for 50 bucks less.