I want some Kahlua, it sounds so good.
Take it from me, mixing alcohols will not make a difference. I've had many a night of beer, liquor, beer, wine, liquor, beer combos, and it's been fine. I've been fine. Actually, the sickest I've ever been was when I was knocking back shots of Jameson like it was water (it's not, it's whiskey, and a good one at that), and while I didn't vomit, I had a hangover for the whole next day.
Also, frats and ambitious college kids make jungle juice all the time, which (for anyone who doesn't know) is like beer, liquor, and mixers all combined in a giant bin or cooler or whatever. And people have been fine off of that. For the most part...