For Deskjet 6940 and most pcl3 printers these days work with OMNI HP BusinessJet 1200 which prints upto 1200X1200 dpi.
There are a few things the driver lacks
no photo cartridge support
no hardware nor software duplex support
For graphics set drivers mode to "24 bit blk & 3 color" and dither to "stucki". As I suspect your printer will further interpolate image and prints it at 4800x1200 dpi.
eCo Software have created several web-sites:
eComStation.RU - News and articles (the 2-nd by visitors)
eComStation.TV - video clips and interviews DevCon - for developers