Hi there - still having a nightmare with this I'm afraid
I have tried the following - running the 1.2.3 Firmware Upgrade Tool in a Virtualbox machine, as instructed near the top of that linked post. However this doesn't seem to work at all - partway through the process, the USB device disconnects from the VM and sometimes crashes completely, after waiting 10 minutes or so just in case. Potentially corrupting my X5 even further
After this, just out of interest I tried booting into standard recovery mode, which worked temporarily.
So then I tried to flash twp_recovery with rkflashtool, exactly as in the guide above (and as I have tried before). No dice once again - just a blank screen in recovery mode, whether I try and boot into "normal" recovery, or TWRP.
I think the problem is still this - my X5
thinks it is running a custom kernel (it is listed in the settings app on device), but it isn't, because I tried to install it before I had TWRP or root installed. Have I totally FUBAR'd this??
EDIT: After tweaking a couple of settings in VirtualBox, I think I have successfully and fully flashed a stock ROM.... Progress!