If you scroll up a little on the google books link it talks through what a clay body is and such and such. Couldn't get it to link to the right page... but go from page 139. It is worth a read as it goes on to talk about lots of different clays.
I was under the opinion that stoneware doesn't exactly vitrify but just gets dense enough so that it's not really a problem. Vitrification is a term to do with glass and porcelain does turn into glass. I don't know if you fire earthenware till it just becomes a glass makes it waterproof. Sounds possible but never tried it.
I have one digital controller for the big kiln but it just has ramp 1 where you put in temperature and time then ramp 2 where you just input top temperature and a hold function. Not very fancy but I don't think my glazes are that fancy I would like to experiment with cooldowns but that will have to wait till I get cash to spare.
Why cant you just add a few test tiles into your larger kiln when firing a load? I find they fit in well in those small spaces I can never get to disappear. Just got to time tests with a glaze firing.