SInce ROCK is able to support internal (will be reformatted) and external storage…is there a clear PRO for one of these options?
no, its entirely up to you
I have chosen an internal SSD for simplicity and availability/reliability.
I have a NAS for backup, with RAID and all the trimmings, but it is sometimes busy with other work.
Ready to ROCK…just bought NUC, RAM and M.2 SSD. Still debating whether or not to buy a HD to use for internal music storage or leave music on my NAS.
If I may know which NUC did you go for?
NUC6i5SYH. Amazon had a deal on them for few days so I jumped on it.
Me too!
No pressure to the developers of course 
Thanks for the info! Think I may follow in your footsteps and buy the NUC and get ready to ROCK! Tired of running the DS 916+ and not being able to enjoy 24 / 192 without dropouts! 
Surprised to hear you’re having dropouts playing 24/192 files. I have been able to play 24/192 over Wi-Fi on my DS713+ without any drops. Even using DSP to upsample to max PCM there are no drops.
No Such luck here! Even though Nas / router / Player connected via CAT 7 Cables. Posted this problem in the forum and the most probable cause seems to be the size of the library. Over 100k tracks. So looking to put the core on the NUC and dedicate the 916+ to storage only!