You will get different answers to your question regarding the best way to prespray. I have always presprayed with a sprayer because it is faster. I keep a stronger mix, for tough spots, in my shampoo tank on the rotary.
For residential scrubbing, prior to hwe, I like this:
http://www.powr-flite.com/product/11%22 ... y=ourPicks
For commercial scrubbing, prior to hwe, I use either a red or green scrub pad, depending on the gauge of the carpet.