Diet will cut you up bro,Isolation exercises might bring out more detail and use higher reps but i find it is the diet i get the results from whether i use bent over rows or chins or someform of pulldown.
Tag is right.Diet bring out the cuts and the training bring out the definition.As for cutting the back up,i thought you might want your whole body to be cut up,lol.Would look kinda silly,back all cut up and nothing else.
Time time and more time,Rome wasnt built in aday and neither will the detail in your back,i have found that each time i have dieted the quality is much better and the fat dosnt store on the body so easy,just my ten cents worth.Good luck!