I'm installing Plex direct from the Package Center within DSM - Plex Version: 1.10.0.4523-648bc61d4. I'm running the latest version of DSM.
NAS Information:
Model - DS716+II
CPU - Intel Celeron N3160
Clock Rate - 1.6 GHz
Cores - 4
RAM - 2048 MB
DSM - DSM 6.1.5-15254