Yo creo que la manera más fácil para meter la Estable es via app, no? Solo que la ROM será en ingles y no GLobal
http://en.miui.com/a-232.html
Download the latest MIUI ROM file
Download here
There is no need to do it again if you’ve already downloaded the latest ROM file.
Connect your device to the Windows PC/laptop via a micro USB cable, and copy the ROM file downloaded in Step 1 into the folder ‘downloaded_rom’ in the internal storage of your device.
Launch ‘Updater' app on your device：
MIUI 6/7/8：Click the ‘…’ icon at the top-right corner, select ‘Choose update package’, and choose the ROM file you’ve put in ‘downloaded_rom’ in Step 2.
MIUI V5：Press the Menu button, select ‘Choose update package’, and choose the ROM file you’ve put in ‘downloaded_rom’ in Step 2.