Mark, I have successfully scanned using your system setup as a guideline, I am running parallels 11 and Running Windows 7 64Bit. The Extending Monitor deal was a lot of trial and error, but can tell you a simple find here, with the Mac OS X world.
Simply change the dual monitor settings on the Mac Display preferences, make sure that "mirror display" is unchecked and go to the Arrange tab and position the monitors side by side, it's at this point, I realized how powerful this was, it seems anything I did on the Mac preferences first, Parallels would follow suit, as soon as I did this, switched over to the Windows 7 side and sure enough, there were my dual monitors sitting there ready to adjust the resolution, of course "Extended" and I set the 2nd monitor up for 800x600 and Viola..... scanning, calibration, everything WORKED !!!!

my first scan

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