Yippee, I've tried again. Single and double starter experiment
This weekend, I made four loaves. Two of them I used straight SD starter and the other two I used double starters (SD and water roux). I had deducted the amount of flour and water from the original recipe to make the water roux starter. Didn't change the hydration level of my SD starter. Guess what? They turned out pretty much the same. The only difference was the flavor. Once again, the loaves made of double starters had almost lost most of the sourness! I prefer my SD with a bit of sourness so my conclusion is to do SD bread with straight SD starter; sweet bread with the water roux starter.
Here are the crumb shots of both of them. I took the picture of the single starter at night so it looked a bit darker but in reality there's no difference in colors.