So, are you getting the 'x''s (errors) as it writes a newly formatted disk after a good transfer? I had a batch of disks (new old stock unformatted and old Verbatim PC ones) that were all bad - they formatted fine, but attempting to write images to them produced errors (the errors in writing were still there, when I used my ][+ and different disk images and cleaned the drives, so it was the disks). Going to a different batch of disks (Kodak DS/DD and Memorex this time, instead of my cheap, Chinese, bulk DS/DD and the Verbatims) gave me good disks - everytime.
I just did this over the last weekend, breaking out the IIc, after getting my ][+ working.
I'm going from a MacBookPro to the IIc (ROM 0, internal drive) making a set of original disks from .dsk images, using ADTPro.
I start the IIc, using speediboot (to guarantee connectivity and free up the disk drive).