Their reply to me:
"Thank you for getting in touch with us.
There have been some issues in the past when powering monome grids with our 6U Bus Board.
Our 6U Bus Board has the following power specs:
+12V 1.4A
-12V 1A
+5V 1A
In order to use your grid with our Bus Board, we suggest that you use the external power supply module developed by Monome called Switch.
This will allow you to power the grid with a wall wart and prevent any stress on the 5V rail.
If you choose to not use this module, turning on the power of your system with the grid connected to the system could damage our Bus Board.
On start up, the grid draws a lot of current and this overcurrent can cause the 5V rail not to work.
Monome has provided some information about powering the monome grid in a eurorack system found here:
http://monome.org/docs/modular/switch/"