I'm not sure if i get your question right . but if you have any kind of effects for vocals and ... mics should go to effect device , then to speakers. organ is like that too ! and if the organ's sound is played in a big hall , recording it with micriophones provides you so much hoooooom sound. to get a clean sound you must record it from a short distance , then apply the reverb you want with another device .
if you want to mix the vocal sound and the organ sound , each microphone should go to a mixer , organ too . they go to mixer's input . and you can connect your speakers to mixer's output . I still think i missunderstood your problem