So after vigorous testing =D, finally. I have 2 receivers, they work perfectly fine. Basically I did what I posted just earlier.
All Patches can be found in their 8Bitdo forums, they are stickied in each forum.
Beta Patches
Patch for Receiver Direct link:
http://forum.8bitdo.com/forum.php?mod=attachment&aid=NTMxfGYxNjBlMTQ0fDE0ODgxMDI4NTN8MHwxNDA0
Patch for Controllers Direct link: FC30/NES30/SFC30/SNES30 Controllers
http://forum.8bitdo.com/forum.php?mod=attachment&aid=NTMyfDI4MTAwNmUzfDE0ODgwMTgzNjV8MHwxMTc5
Easy steps after patching:
1. Plug receiver in player 1 port.
2. Plug wired controller in player 2 port.
3. Turn on NES Classic
4. For the 1st 8bitdo device, hold start to begin pairing mode. The receiver should also be blinking blue LED.
5. When paired should be solid blue on each.
6. Go to a game that uses RetroArch, once game is loaded hit (default Start+Select to get into RetroArch menu) on the 8bitdo controller.
7. On wired controller in player 2 port, navigate the menu: Settings > Input > Input User 1 Binds.
8. Go down to the user bind for directional, tap A on controller 2 to allow you to enter new binding, then on 8bitdo controller tap the corresponding direction.
9. Follow steps until all directionals are set on controller 1.
10. Confirm now with 8Bitdo device that you can move up and down through the menu.
*Steps below are only needed if you have 2 receivers like myself
11. Unplug 2nd controller and plug in 2nd receiver and pair that with 2nd controller.
12. Once paired, this time use Controller 1 to go back 1 menu to Input Menu, this time select Input User 2 Binds.
13. Follow steps from 8 to 10.
14. Presto, both controllers are now functional, enjoy your gaming
*PS I am not 100% sure if you need to do these steps if you re-flash due to the Retroarch configs get wiped. (If I am wrong that could be only if you re-flash RetroArch itself, if you just add games it should not affect it.)
As I stated I have one SNES30 and one SFC30, the reason I bought one of each is so I can differentiate between which one is Player 1 or Player 2 on the receiver, instead of labelling. Both cost the same when I bought it so.
I hope this helps with setting the controls up with it. If you need more help after this let me know =D Completed like 4 arcade games with some friends today, was fun