It would appear that 94.3 could slide eastward almost 20 miles and not be an issue with 94.1 in Providence. It woud cause it to be further short-spaced with 94.3 New Haven, but since most of that's over water, that could probably be handled with a directional. I am, though seeing some short spacing approved that is way inside the FCC requirements. For instance, here in NE Ohio, WKDD was recently granted a move to a transmitter site in Cuyahoga Falls. That's less than 10 miles away from 3rd Adjacent Class B WONE on 97.5 and less than 20 away rom 3rd-Adj. Class B WNCX on 98.5. With some creative engineering and a DA, I'm pretty conident that WFME could move to the ESB.
There is a very, very big difference between the Ohio example you cite and this case, though.
What's now WKDD on 98.1 was allocated before 1964, as were the stations that are now WONE and WNCX, and those stations have remained short-spaced to each other ever since. As a result, they're eligible to use the provisions of 73.213, which has no restriction on spacing between grandfathered second- and third-adjacent signals. If there weren't other factors at play, 98.1 could have moved all the way into the Seven Hills/Parma tower farm without having to worry about WONE or WNCX.
As has been explored pretty extensively here by Play Freebird and others, WFME doesn't have that same luxury. While there is indeed some "creative engineering" that could be done to make WFME work at Empire with respect to another big obstacle, co-channel WMAS-FM Enfield CT (especially if WFME is purchased by WMAS-FM's owner, Cumulus), it was Freebird who first noted 73.213 does not apply
to the WFME/WIGX spacing. While both signals are pre-1964, they're not grandfathered short-spaced because they're not short-spaced under the current rules (73.207). And without being able to use the grandfathering provisions of 73.213, you have to turn instead to a different set of short-spacing rules, 73.215...which includes a mileage-spacing table that makes it very clear that WFME-at-Empire and WIGX don't qualify, DA or no DA.
And, again, there is no room on the Empire mast for a separate directional antenna, nor would it be financially feasible for a single station to pay rent for an FM antenna aperture there, even if room existed.
Laying all that aside, WIGX is already egregiously short-spaced to WYBC-FM, and the rules don't allow for that short-spacing to be further increased, either.
(On another matter, I'm also not fully convinced that a booster would be the right answer for WFME, either. Boosters are great when there's massive terrain blockage between the main site and the booster, which is why they're mostly seen out west. In Salt Lake City, for instance, there's a site 60 miles out of town that was specifically designed to be completely blocked from the core of the market by the Wasatch Mountains in between. That allows for powerful boosters to "fill in" the signal over Salt Lake City itself. But in the case of WFME, there's lots of WFME RF that gets past the skyscrapers to the east side of Manhattan and beyond; it's just multipath-distorted and messy. Throw a booster against that and you're only adding to the mess, as WFUV and WFMU have been learning with their own booster attempts in Manhattan and Brooklyn.)