Last I heard, unless you're an established author with large sale counts, you don't get an advance anymore. Those days seem to be long since gone. At least that's the last information I have.
Either way, unless you have a really good lawyer, a killer book, and a pension for being treated like dirt, I'd avoid the big six. Of all the good/bad stories I've heard out of them over the past couple years, 99% have been horror stories, or just bad, and only 1% have been good. It's what originally drove me to go small press at first, and then eventually indie when ebooks became mainstream and began outselling my print books hands down. With ebooks the way they are now, and the power the indie author has at their fingertips for marketing and self promotion, you're better off going indie these days.