I didn't have a proper amaro, so I used equal parts decaf espresso, Jägermeister, & Tia Maria, with a lemon zest twist (expressed & discarded). Surprisingly good!
Even with equal parts, the Jäger hides the coffee a bit, so I'll try 30/20/40 next time.
I only had 15ml lemon juice (due to a Jack Dempsey), so I subbed 5ml gin. To my surprise, it was still a bit sweet (is that because I used agave nectar?). After looking at the original recipe, I added another 15ml gin (total of 50ml), and ta-da!
Plymouth Gin, Tia Maria, medium roast decaf espresso, homemade saline solution, and a full barspoon of Agave nectar—this one is quite nice!
Still... It needs something. Perhaps a bit more body?
It's probably the dry gin, as you say, but I wonder if the Plymouth would meld better with the more-complex Galliano Espresso than the Tia Maria, which is a little thin.