The following worked with my Synology NAS:

1. Browse to the network drive in Finder
2. Double-click on the sparse bundle file for the computer you want to access.
3. Click on the "Time Machine Backups" disk image in Finder (added to the left-hand pane by step 2 above).
4. Open the backups.backupsdb folder inside this disk image.
5. Continue as per previous comments.

The following worked with my Synology NAS:

1. Browse to the network drive in Finder
2. Double-click on the sparse bundle file for the computer you want to access.
3. Click on the "Time Machine Backups" disk image in Finder (added to the left-hand pane by step 2 above).
4. Open the backups.backupsdb folder inside this disk image.
5. Continue as per previous comments.