hi,
I have the same F4-220.
BTW mine have 5th hidden sata port inside which makes it F5-220
I have successfully installed latest DSM_DS918+ 6.2.3
The key to success is to install driver extensions.
pat file :
https://global.download.synology.com/download/DSM/release/6.2.3/25423/DSM_DS918%2B_25423.pat?model=DS918%2B&bays=4&dsm_version=6.2.3&build_number=25423
driver extension:
http://s000.tinyupload.com/?file_id=05072313334244665017
During USB boot drive creation mount second partition and overwrite extra.lzma and extra2.lzma
After uploading PAT file the NAS will restart but it will not show up on a network ( this happens just once after initial installation). Unplug the NAS from power and plug it back.
From now on it should work just fine.
I can confirm HW transcoding works
I haven't manage LEDs to work ( stays red)
Good luck
(let me know if your NAS have the 5th sata port as well)