To begin with, sorry for my bad English. I’ll try to do my best !

How RME's Manual blew my UCX :

Last week, I had to use my UCX on Windows to quickly check something before leaving my office.
I was remembering something wrote in the Manual as a Feature "FireWire and USB can be connected at the same time" and would works, but “not recommended” supposed for 24/24 usage. Nothing mentioned about the fact it could totally destroy your FireFace and doing it fast !

So I used my MacBook Pro without turning it ON (with Apple Power Adapter plugged), which can power the Unit without using the DC adapter, and connected the USB cable to my Windows Desktop Computer for Data.
When I started my Desktop Computer, all UCX LEDs powered correctly ON but faded a lot like if they had difficulties and a huge power draw for 3 seconds before a total blackout and no more life sign.

At this time, a bad burnt plastic smell came from my UCX.

After a lot of fear and approximately 30 seconds (time to cool down ?), I could restart normally my UCX ONLY through the FireWire Bus Power and Power Switch on OFF position, but the Host red LED stays ON. The device cannot anymore connect to the Mac through FireWire only. I had to use in addition the USB cable to get it detected and working.
The Internal Power Stage can’t no more power the Unit and seems to be Down (tested with one different RME AC Power Adapter from my QuadMic II and checked functional with a multi-meter).

I think that only the FireWire Controller and Internal Power Stage blew due to ground Voltage difference/ground loop/or shorts (supposed) ?
All firmware are still visible with Flash Update Tool with USB connection.

From your point of view, what do you think I can do to check it and get it working back ?

Nothing in the Manual mentions the fact that the thing I was trying to do is bad and can cause fatality for my FF UCX…

Many thanks and Happy Christmas Holidays !