EPSON WF 7720 Transparancies
Try the "Premium Presentation Paper Matte".
Myself and many others have had the greatest success
with this setting.
Additionally, be sure and Un-Check "High Speed"
under the More Options Tab.
In the Epson print menu:
Media type- Premium Presentation Paper Matte
Print Quality- Best Quality
Don't check greyscale
Color Options Manual Settings, Mode- Adobe RGB
Color Matching- Epson Color Controls
The latest test I did that produced great results was from an RGB artboard in illustrator with black set to c- 75, m- 68, y-67, k-90.