Maracyn PLUS contains sulfa drugs which are excellent "broad spectrum" antibiotics. (Meaning that it will treat a wide variety of bacterial diseases.) IMO, it was a good medication choice.
On one hand, since he's survived for two weeks, it's likely that the Maracyn PLUS has been helping (since most fish with dropsy don't survive that long). On the other hand, the PLUS may have already done all the good it's going to do.
Since you've already started the Kanaplex, I would keep using it. It's also "broad spectrum," and is excellent at treating internal bacterial issues.
That said, I usually don't recommend using two antibiotics simultaneously. Medications are metabolized by the liver and excreted by the kidneys. "Doubling up" will cause a lot of stress on these organs.
You didn't mention any other symptoms. However, he's eating well, which is also unusual for a fish with dropsy. Have you considered internal parasites? If he has them, then metronidazole/praziquantel may be a medication option. The metronidazole will also treat internal anaerobic bacteria.
How much Epsom salt are you using? And for how long have you used this dosage?
If 100% water changes are stressful for him, I would do daily partial ones instead. Also, how well covered is the tank? If there are openings, you can cover them with either plastic food wrap (Saran/Glad) or aluminum foil. This will increase the humidity level, and make it easier for him to breathe. (I know you've lowered the water level, but I'll mention that there should be several inches of air between the wrap and water, in case other people are following this thread and want to try this with their own fish.)
You may want to send a PM to Sakura8, and ask her advice. She has a vast amount of fish disease and medication knowledge.
@Anhel - Regarding your recommendation of using Jungle Fungus Clear. Fungus Clear contains two furan medications (nitrofurazone and furazolidone).... The OP mentioned using medicated fish food. If this is the Jungle brand of medicated food, it contains sulfathiazole and nitrofurazone. So it has both sulfa and furan medications in it.