You can use the Epson profiles with InkThrift ink in your 3800, though the output will not be color matched (this is fine for some people, depending on the application). To optimize your output specific to the printer, ink, paper and print settings you wish to use, we can make custom profiles for you, or you can get a profiling system to make your own ICC profiles at home.
Since we don't have pre-made InkThrift profiles for the 3800 like we do for several other printers (generic matte and gloss profiles, which work to get decent results with a range of matte, rag and gloss papers), I would be willing to make you one matte and one gloss custom profile for free, which I will then post for others to use. Are you printing from a Mac or PC? What Operating System and Photoshop versions? What papers do you use? Please let me know, and I will email you everything you need to have the two free custom profiles made.
Best regards~ Dana