I had the same problem ;here's the solution.
Plug only one of the cables in at once.
ie.If you want input , plug in the in cable.
If you want output plug in the out cable.
The poly800 and ex800 dont have midi thru ,
so it wont work with both cables plugged in.
Plug only one of the cables in at once.
ie.If you want input , plug in the in cable.
If you want output plug in the out cable.
The poly800 and ex800 dont have midi thru ,
so it wont work with both cables plugged in.