well, it's more a question of vowels...rounding out the vowels will help create a more uniform blend. the other thing would be to have less vibrato and more straight tone. certain consonants will also have to be indicated when they're cut off and etc...i could probably create something to help with this depending on what's needed in terms of "lyrics". OA, hit me up, i do have experience in choral writing and can help weed out any problems that may arise.