First: Thank you for your great work! I'm using primary linux OS at home and your lib is a great way, using the Dell C1765 printer with it!
Now, I'd made some tests and see also some quality differences between windows and linux. Not big but visible.
You wrote, you need a icm file for supporting the printer better? I looked online and found under the URL http://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=103KJ
the download "Dell C1765nfw Color MFP Software Suite and Drivers". When you extract the file, you'll find inside the file dlthm1z.cab (subdirectory \English\HB\Win_87VistaXP\x64\). It contains some dll's and a file dlthm1zPL.icm. I think thats the file you mean?
So far I understand right, the file only support by computing colours right.
Is there maybe also a way, enhance the driver with some options for the print resolution?