Hello thdetdestro
I can understand your frustration in not being able to utilize your switchable graphics on your HP ENVY m6-1158ca. I am going to go over some things that I would like you to ensure that have have completed in order.
*** NOTE: Be sure that you have the Notebook plugged in and you are not running off the battery during any of the process
First, under Windows 8.0 on the HP Driver site you will see a BIOS update that will bring your BIOS to version F.25. Are you currently running the F.25 version of your BIOS? If not, I would suggest we revert back to Windows 8 and ensure that we run the BIO update located here.
Second, after installing the Windows 8.1 Update I would like you to ensure that you go to this page and ensure that you (start with the Chipset Drivers) install ALL the drivers for your HP ENVY m6-1158ca.
Now, if you run into ANY errors I would like you to document them exactly (a screen shot is best if you can) and re-post with the error and a description of what part of the process you were at.
I hope this resolves your Windows 8.1 and Switchable Graphics issue. I would like to thank you for posting your issue here on the HP Forums. Have a great day!