Speech is known to be a problem in many games, right now. Yes, the ePSXe team is working on improving the internal SPU for the next release. That may fix some of the speech problems.
But, there is something that you can try. Try using Pete's CD plugin and set the speed limitation to 2x. This is the speed of an actual PSX CD unit. Then try using which ever SPU plugin you prefer, and see how speech sounds. That is what I did and speech has improved a lot. I use either Pete's Midas SPU or the internal SPU. Null2's SPU won't work properly for me at all. Best of luck.