For firmware check this thread...
http://www.rcgroups.com/forums/showthread.php?t=2486545
The various bits and pieces developed mostly by Povlhp, ThomHpl, DBorthwick are collected by benb0jangles here...
https://github.com/benb0jangles/FlySky-i6-Mod-
The official firmware is here.
FS-i6-Update-20151015
点击下载
on this page...
http://gb.flysky-cn.com/download_detail/&downloadsId=23.html
Probably you have the latest. Not sure why it's not on the English download page since they revamped their website. You can download the "latest" (I'm guessing) FlySky firmware from the Chinese site although I'm not sure if it is English language. I suspect it is... The Turnigy version is on the HobbyKing website somewhere - probably the files tab on the i6 page of the international warehouse. I believe they work interchangeably but I haven't tried.
- I'm not sure the sim adapter cable is necessary either but one comment said that set did not come with one that works with the i6 so it seems worth pointing out.
- Where are you getting the custom springs? Is there a bulk price?