Speaking of detection, it's true the game will ONLY notice the R7 graphics since the RX 460 is more like an add-on graphic cards and NOT the switchable graphic card which turns on when certain apps (or games) activate it.
But since you have an issue of low fps, you can follow these steps:
(Make sure you have the NET 3.5, all VC Redist and DirectX installed before)
1. Clean uninstall all AMD drivers (download the tool here: http
/support.amd.com/en-us/kb-articles/Pages/AMD-Clean-Uninstall-Utility.aspx)
2. Download the Radeon Software (link: http
/support.amd.com/en-us/download)
3. Choose Manually Select Your Driver -> APU (Accelerated Processors) -> Mobile APU (Accelerated Processors) -> FXtm 9830P APU -> Select your OS -> Display Results
4. Download the Radeon software (current driver at time of this answer, release date: 5/4/2017, Crimson ReLive Edition 17.4.4)
5. Install the Radeon Software
6. Just follow the installation procedure, next, next .. wait for installation to finish
7. Restart computer
It works for me, and my X550IU works flawlessly on both gaming and usual computing.
Cheers!