This might be a bit more than you want to spend - I don't know your budget for this. But... the Presonus Eureka channel strip has a cool 'Saturate' circuit on the front end of the pre. It's essentially an asymetrical dual-FET thing, that alters the drain current from the input transformer.....or something, from what I've read. I have no idea what that means. It's sounds really good though.

You should be able to pick one up for under 300 bucks.
IIRC the MixSaturate plugin didn't really add "grit" like an OD pedal would, so maybe this is your solution as the Presonus saturate function doesn't add 'drive' either.