Thanks for feeding back.
I have more details, and what looks like a cure for me! Details posted here in case anyone else has similar issues.
I was looking for clues as to why the Samsung LCD panel would stop working.
All my devices (keyboard, mouse, headphones, oculus rift & sensors, monitor usb hub and powered external hub, G920 etc.) were distributed evenly between the "Intel" and "ASMedia" USB controllers.
Since using new headphones I could regularly hear disconnect / reconnect windows sounds.
Looking for clues I was watching device manager and observed both the Samsung LCD and Oculus rift sensors were dropping out.
After "random" trying the LCD in different ports I unplugged everything and went through a process of elimination to work out which devices (and hubs) worked best on each port. This took around two hours!
1) Keyboard & mouse, USB 2.0 ports. This wasn't a configuration change but is worth keeping in mind.
2) Samsung LCD stopped dropping off when it was plugged directly onto the "Intel(R) USB 3.0 eXtensible Host Controller".
3) USB headphones would not detect in windows if they were plugged into the adjacent port to the LCD.
4) Oculus rift sensors were repeatedly disconnecting and reconnecting when plugged into ASMedia controller(s) and issues reported by oculus software. Move to "Intel(R) USB 3.0 eXtensible Host Controller" and no more issues reported.
5) System has been stable since moving all devices onto the "Intel(R) USB 3.0 eXtensible Host Controller".
6) Rift sensors plugged into powered usb 3.0 hub (Anker)
7) Monitor plugged into powered usb 3.0
8) Headphones & Game controller plugged into monitor (don't judge, it's the most accessible cable point!)
9) G920 & Oculus rift direct connect to rear ports on motherboard)
I hope that helps anyone else out there!
Motherboard: Asus Rampage V Extreme