Hey man I really appreciate the info you're giving here. I'm always grateful to learn from those who've reached a level I hope to one day.A good way to get those contractions down in the back is to practice cable pulldowns. Just practice "pulling" down w/o gripping the bar attachment. I just rest my palms on it and press down thru my palms w/o gripping it with my fingers and do that circling the pie pattern that engages the lats properly.
Another good movement for me to get the lats firing properly is to do cable lat pulldowns with a single D handle. So do them iso laterally. I dont sit on the seat. Too big for that. A smaller guy might get the proper stretch but i cant. The cable tops out in that position before i get a full stretch. I kneel on the floor and allow the weight to pull to a FULL stretch then initiate the movement going back down FIRST with the lats. I feel like a chicken being pulled apart. Let the lats take the brunt of the stretch. And finish the pull with the lats. Too easy to let the biceps take control. Doesnt take alot of weight if your lats are doing it especially at first. I do these supinated btw with the D handle
If you ever end up with a few minutes, I'd be really interested to see what you've found for a specific program you like. Currently I'm doing Dorian Yates routine from 1987-1992, I posted it in either the bodybuilding or training section a few weeks ago. I only made one tweak which was subbing hammer strength row in place of barbell row. Even tho I love rows, I don't get nearly the same contraction as I do with the machine.