1. - USB/SPDIF converter into DAC
Have anyone compared JKENNY HIFACE MK3 and AUDIOPHILLEO 2 ?
Which one is "better" ?
2. - MAC MINI + TOSLINK cable into DAC ?
3. - Streaming into DAC ?
Which option should be choosen ?
With regard to all 3 options, I don't think one is clearly the best.
It comes to personal preference for type of computer environment and whether or not you like / dislike UPnP streaming enough to go that route.
I think for the rest you will get a lot of biased opinions for any of these options without anyone able to "prove" which one is best. All options will have their followers.
Best to try for yourself and / or see if you can have a listen with other peoples setup.