An "on-the-fly" Cylon voice converter is really "the Holy Grail" of classic Cylon costuming - so far there is no perfect solution for getting THE classic voice
There are a few good options and some more in the works. I don't know any links, or info off the top of my head, but there are a few around the web / some kicking around here in older threads.
For my suit, I am planning dual sound systems. One system will run an MP3 player for the "eye sound" just looping over and over. Lower volume, speaker probably pretty small (the eye sound should not be BLAIRING ya know... you don't hear the eye sound from across the street). And then a separate sound system for some voice changer. Hoping to find one with a boom mic inside the helmet that will cover my own voice enough - with the help of a larger "more powerful" speaker. So far I'm still looking too.
Now, you could use a setup with just classic phrases. Have a Cylon sound board of sorts that you could run via switches in the gloves or something... maybe music too? But that wouldn't get you a "voice" to talk with, like at a convention or something.
I'm still looking too - so we can help each other!!!
P.S. One thing you GOT to know right up front - the "real estate" inside the helmet is SMALL. Not like a Stormtrooper, etc. with some room for extra gizmos. Most of it will be filled up with your head - the Mohawk gives room for some gizmos and extra items, but not much. The eye scanner takes up ROOM... and visibility is AWEFUL / Next to nothing... Isn't that great?! Gotta love Cylons
LOL! Besides the eye, I'm only planning on a tiny fan being in my helmet. The rest of the electronics will be somewhere else in the suit.