Simmer the Splenda and water, stirring only once, for 5 minutes. While that is simmering start whipping the egg yolks in a stand mixer. Once the sugar has simmered for 5 minutes and has started to thicken slowly pour it into the egg yolks while still whipping.
Whip until room temperature and tripled in volume.
Add the mascarpone cheese and 2 TBLS chocolate syrup. Whip until thick and creamy.(The mixture will seem to break at first, but continue to whip and it will come together.).
Fold in the Cool Whip and place in the refrigerator.
Simmer the coffee and the 1/4 cup chocolate syrup until combined. Add the rum and coffee liquor, simmer for 2 minutes. Let cool for about 5 minutes in the refrigerator.
Rough chop the cherries.
Take the mascarpone mixture and coffee mixture out of the refrigerator. Dip the lady fingers into the coffee mixture (allow the coffee to just soak through the cookie, not too dry, not too soggy) and place in a single layer on the bottom of an 8x8 square baking dish. Top with half the chopped cherries then spread half the mascarpone mixture over the top. Continue with one more layer of the soaked cookies, cherries and cream.
Cover with plastic wrap and refrigerate for at least 2 hours.