Its very hit and miss getting a DM600 to work with an external card reader.
I gave up with mine in the end and have got another DM7020 so i can use the second card. picking it up on Saturday
The problem i have had with mine is that if the reader is connected at reboot the box refuses to boot up and after you connect it after the box has started to boot sometimes it sees it sometimes it doesn't
Complete waste of time in my opinion, its too much hassle. I know the problem isn't with the reader as it works fine with my 500s.
Nano