colno9,
You may know this but since you don't mention it in your post, inkjet inks are transparent, with the exception of black, which can be opaque at full density. As a result, the more black ink that is used in dark colors, the more opaque it will be. Epson just released a new CrystalClear film but it is not adhesive backed. The other issue you will have to deal with is that any white space in your image will be clear when printed on a transparent film as there is no aqueous-based white ink. I am not aware of any adhesive-backed material that can be printed on your Epson, but maybe someone will chime in with info about such a film.
I spent many years supplying the solvent and Eco-solvent media market. There are clear adhesive-backed vinyls available for these inks that are often used to print signage, which are then laminated over other substrates, such as reflective material for the production of traffic signage. When the printed clear film is applied over reflective, metallic, holographic, etc. films the ink allows the substrate to show through so the reflective property of the film causes the colorant to take on the property of the substrate. For example, if you print a red stop sign on clear and laminate over DOT reflective film, the red becomes reflective. I hope this makes sense.
I would suggest that you evaluate some prints done on the new Epson CrystalClear film so you can determine if the look is what you are targeting. If you like the result, this material can be mounted to Plexi using an Optically Clear double sided adhesive.
