Actually, I seem to remember running into the same issue. Make sure that you're running it from an "elevated" command prompt with administrative privileges. I seem to remember my error having something to do with the way I was typing the command in. I could be wrong, but I "think" what I did to work around it was mount the emuMMC partition with a drive letter, and then pass that drive letter to dd rather than \\?\Device\HarddiskVolumeXX.
I did mine slightly differently because just as a matter of preference I like having my emuMMC partition at the beginning of the card instead of the end, but that requires deleting the partition afterwards and is a little advanced.
If I can find a spare microSD card laying around, I might try playing with that dd command some more just to verify what I did to get around that error message.
You're really close to having Atmosphere + emuMMC, don't give up yet!
yes i run it with administrative privilege from CMD and powershell and both didn't work