I am running the same exact setup as you. I run PlexServer on my main Ubuntu desktop with all my media files stored on Synology. You don't want ssh for this. You want to mount the Synology to Ubuntu via SMB or NFS. I prefer SMB as it's giving me less problems over the years.
OK lets do this (and PM me if you need more help):
Make sure CIFS support is enabled in your Synology. Goto Synology » Control Panel » Shared Folder » File Services. Make sure Enable SMB Service is enabled. My Workgroup is "WORKGROUP" and the other checkboxes are disabled.
Now on Ubuntu, you can check this by opening the File Browser and clicking "Other Location" or "Connect to Resource". You should be able to type in the address: smb:/<SYNOLOGY_IP> and it will prompt you for your username and password. If that works, we're good for the next step.
Create a new directory on your local system at /media/Synology and make sure you own it. "sudo mkdir /media/synology" then "sudo chown $USER.$USER /media/synology". It will be empty for now.
Edit fstab by typing "sudo vi /etc/fstab" on the command line. When you have that open you just need to know that typing like normal will not work. You first need to hit "i" to get into "insert" mode, then you can type like normal. Hitting "esc" will leave insert mode, then you can hit ":q!" to exit without saving or "Shift+ZZ" to exit and save (Yes vi is weird). -- Hit i to enter insert mode. Add the line like the following at the end and save (change all required variables in <>).
//<SYNOLOGY_IP>/<SYNOLOGY_VOLUME> /media/Synology cifs user=<SYNOLOGY_USERNAME>,pass=<SYNOLOGY_PASSWORD>,iocharset=utf8,uid=<UBUNTU_USERNAME>,gid=<UBUNTU_USERNAME> 0 0
Whew, almost done. You should be able to simply type "sudo mount -a" which will mount the Synology folder to /media/Synology.