Hi,
I have a rPi 2 with an Audiophonics ESS DAC board, running for the past 5 years. Why am I telling this? because I experienced Volumio as a stable platform for the past 5 years. If you mean by “stable” a software, that is not crashing, then yes, volumio is stable.
If by “stable” you mean feature-equivalent to big-industry solutions (Sonos, BlueOS, HEOS etc.) then the answer is no. But this has never been the intent of volumio. Right now, volumio offers working integrations of Spotify, Tidal, Qobuz and can either access a network drive or manage files on a directly connected USB drives. You can also stream audio through Bluetooth or Airplay to a volumio device.
If you need a specific feature, be it a more comfortable Qobuz integration, easier ways to add network drives or whatever, than you need to be aware, that volumio is a open source platform, maintained and managed by a very small group of very dedicated developers. Their resources are limited and they have to prioritise, which new features they can implement.
Setting up a rPi yourself is quite easy and you will find all the help you need on this forum. Building a DAC/streamer is no more difficult than snapping together two Lego bricks. Burning the volumio OS onto a flashcard is no big deal either.
If you just want an inexpensive streamer, without building it yourself, look at the bundles from Allo, audiophonics.fr, HiFiberry etc.
A bit more upscale is the pro-ject streambox S2, the S2 more so. Both are running customised volumio versions. The Volumio Primo Box is another option. Moneywise, the miniDSP SHD series tops the list, afaik, but offers quite a few tricks that are independent of the volumio implementation.
Theres a lot out there to choose from and it’s up to you to make a decision - but if you’re not sure, just ask away here. There are lot of knowledgeable people 'round here.