mmm, that’s weird, i’ve uploaded samples with no issues so far (only one being the time needed to do the upload of biiig files :thinking: )
you should be able to upload your samples using the usb port and c6.
make sure that in c6 you select the AR in the config page (MIDI panel) and then either load or drag the sample you want to upload into c6 and then select the sample you want to send.
on the AR you go into the incoming folder of samples (or the folder you created)
click send on c6 and you should see on the AR the progress bar appearing together with the sample name (or progressive numbers starting from 0 if i’m not wrong) should appear in the folder
this works fine for me, hope it helps you as well