I've just done a google search and found a website recommending adding 3 tablespoons of bicarbonate of soda to each litre of water when bathing a dog. Apparently it will help get rid of odours, makes the coat softer and won't irritate the skin.
I'm not sure that you could do that when already using shampoo and conditioner, but maybe when it comes to hosing down a wet, stinky dog you could do a final rinse with some warm water and bicarb?
The ends of Louis's ears get particularly smelly during wet weather so I think I'll try washing them in water with bicarb. dissolved in it and see if it works.