Hi arginine,
I'm sure that you already know that using RuneAudio is as easy as writing an image to a SD card, so I suppose you don't have any SD left laying around your home... or you are too lazy to try it

Anyway, here there are the informations you requested, in order to be useful to others with the same questions.
Please mind that, in the following points, I'm always referring to the last (coming soon) 0.3-release, that can be considered as a milestone and represents a leap from the past (and from RaspyFi/Volumio), as disclosed
here.
1) I can't say if RuneAudio sound quality will be better or worse to you. The only way to discover it is trying by yourself.
What I can say is that Volumio's sound quality comes from a work of research and optimization made by
Orion during our collaboration in the RaspyFi project. He created the so called "kernel profiles", letting users tweak some low-level system parameters to adapt the "sound signature" to the personal taste. Those optimizations are still in development under RuneAudio project, and are reviewed every time the distro is upgraded and a different kernel version is used.
2) Of course you can play music from network mounts, using both SMB/CIFS and NFS protocols. Moreover, the "Add network mount" wizard has been improved since the previous 0.2-beta.
3) Yes, you can play ALAC files, but you have to enable "FFmpeg decoder plugin" first, under MENU > MPD. It is disabled by default due to possible performance issues.
4) Album covers are natively displayed in the main playback screen of RuneUI
5) I2S DACs support is seamlessly integrated in RuneOS/RuneUI and easy to manage. Currently supported DACs are: G2Labs BerryNOS, G2Labs BerryNOS mini, HiFiBerry DAC, HiFiBerry Digi, IQaudIO Pi-DAC, RaspI2SPlay3
6) You can easily install and update packages via pacman, the default packet manager in Arch Linux
I hope to have satisfied your curiosity