Hi,
I was in similar situation with my Redmi 3S (with 3GB ram and 32GB rom). After I had tried to flash global rom several times to the phone it was detected as "Qualcomm HS-USB Diagnostics 900E" by my PC. Then I found out the location of the test points on the motherboard and I managed to get it working again with global stable rom (previous was china stable). My device still has locked bootloader as I'm waiting for unlock permission. Hopefully you can find help to your situation from my post. You probably should clean your device drivers if you have manually forced them to be different. I did not do any manual device driver configuration in my Windows 10, it found the correct ones automatically.
I cannot give any warranty for the information I give, but I got my bricked Redmi 3S phone working with these steps:
- I recharged the battery with my USB charger for couple hours to be sure it had charge
- Disconnect USB cable from the phone
- Removed back cover
- Removed internal cover from motherboard held together by screws (one under MI -sticker)
- Removed battery connector
- Reattached battery connector
- Connected phone via known good USB cable to PC (connect straight to PC motherboard USB ports, do not use any USB hubs etc between phone and PC)
- Shorted the test point pins while holding "power" + "volume down" -buttons until device reboots. I used metal tweezers for mobile phone repair I got from ebay as the pins are small & there are components near.
The device should now be recognized as Qualcomm HS-USB QDLoader 9008
Which means you are back in EDL-mode
- Flashed official Xiaomi global stable rom via miflash with "clean all" selected.
- After miflash had successfully flashed (took around 230seconds on my PC) I disconnected the phone from PC and removed battery connector.
- Reattach battery connector and press power to normally start phone. I was welcomed with normal MI-logo and the first start took somewhere near 15minutes.
The filename for the rom I downloaded from Xiaomi servers was: land_global_images_V7.5.9.0.MALMIDE_20160805.0000.29_6.0_global_470b843c10.tgz
The version of xiaomi flashing tool / miflash I used was "Miflash 2016.08.30.0" I got from Xiaomi flashing guide "method 3. fastboot upgrade" page.
I'm hoping to flash xiaomi.eu rom after I get the bootloader unlocked so I can install TWRP, but now I have again functional phone.

I attached two pictures to this post, one with clear picture of motherboard and one with test points circled.
Photo of the motherboard where I have circled the pins that need to be short out for forcing EDL and battery connector:
View attachment 13699