Synology x25 model NAS are incapable of hardware accelerated transcoding. Synology did not include the necessary drivers in the OS for those systems.
Simply moving the drives to a new Synology NAS depends on the version of DSM, the CPU, and the file system type. In general, if the DSM versions and CPU architectures are the same, then you can move the drives without losing any data. That written, definitely check with Synology tech support first. Also, make a backup of all important data before moving the drives.
Moving Plex to a new System
It is possible to move the Plex Data Folder from one system to another, retaining the database with library definitions, etc.
At a very high level:
From Syno to Syno, use Hyper Backup to backup the Plex Data Folder, then restore it on the new server.
From Syno to native Linux installation, make a backup of the Plex Data Folder with tar, move it to the new system, untar and set permissions.
From Syno to Ugreen, requires additional steps, as Plex runs in a Docker container on Ugreen NAS.
The process is straightforward, but the exact steps vary depending on source and destination systems.
Another option to consider is running Plex on a separate PC, using the NAS for storage. This lets you upgrade compute and storage separately. You can upgrade the CPU running Plex without having to upgrade the entire NAS.
Something as simple as a Beelink S12 Pro mini-pc has the transcoding power of any AlderLake CPU.
If you use the same NAS, connect with SMB (if you use Windows) or NFS (if you install Linux on it instead), you’ll have a lot more life in the existing Syno.
I have a DS1815+ which is still an excellent NFS server for my other Linux test boxes.
This is precisely why in the other thread I’m trying to get the automatic search to work, having PMS already installed in Ubuntu on a NUC with an Intel 13 i3. I’m sure PMS runs better on the NUC, but on the other hand, since I have a large library, I can’t do without the automatic scan.