You are aware that we’re not quite there yet? I mean, Roon is not portable as of now, even if it is on the roadmap in some form.
Anyways, like you I started my digital music experience based on iTunes, and was quite fond of it actually. (I did dabble around with WinAMP and lots of MP3s before that, but that was computer audio. Since iTunes I was able to integrate file based playback as a part of my music listening habits along with vinyl and CD.)
While I adopted AIFF for a while I decided to go all FLAC a few years back, and I haven’t regretted my decision. My habitat hosts mainly Apple products but there are occasional Windows and Linux machines appearing as well as an odd Android.
The only annoying thing is that Apple does not support FLAC in iTunes, or perhaps that’s an advantage. My iTunes library now contain an excerpt of my total library, regularly updated by batch converting additions to .m4a AAC-files in 320Kbps. Perfect for use in the car and on my old iPod Classic also!
(I use EZ CD Converter for conversions and tagging, excellent tool!)