I’ve never used a Squeezebox player, so probably not the most informed to answer your questions.
Yes, but whether it would fulfil your expectations is another thing. You don’t say what these are. There are a couple of plugins in Volumio that would be of particular interest to you (Volumio Plugins Collection): the LMS and Squeezelite plugins.
There are loads of DACS to choose from and if you’re looking for excellent sound at a good price, then i2s DACs are hard to beat. Of course, you can always attach a standard USB DAC.
The big problem you will have in moving to Volumio will be the lack of support for Home Assistant. Both Google’s & Amazon’s automation options are scarce in Volumio; I’m not sure why, but suspect it is a matter of user priorities for their audio experience.
Edit re. Alexa/Home Assistant: also you don’t have the fine control, nor search etc.