28x34 will give you one lower gear than what you've got now. It shouldn't be much of an issue to change the 28 chainring out for a 24, which gives you a lowest gear about 1.5 "gears" lower. That shouldn't require changing either derailer, though it may take some adjustment to get it tuned.
Just make sure, when you switch to your drop bars, to get a 9 speed triple shifter set.