Just a little add on to Bigbadtom excellent reply. As a rule Fenway seating is not great for concerts so no matter where you sit you will be far from the stage and if you are in the far left field or right field corners you will have a bad viewing angle to see the stage. Field box seats are OK, or the State Street Club as Bigbadtom stated. I have sat in Home Plate Pavilion Club for concerts and they are good although far from the stage.
For Loge seats Row AA is the first row and as Bigbadtom said you want to be above the major walkway so I would go for Row DD or higher. If you are looking at home plate area seating you will be looking through the protective netting. Actually protective netting has been added all around the infield area which would mean looking through it in the field box seats. I have not been to a Fenway concert since MLB started to require the additional netting so you might want to call Fenway and ask if they take down the netting for concerts. My guess is that they don't but you can call to ask. Infield and outfield grandstand I wouldn't sit higher than the first few rows, maybe no higher than row 8. In grandstand you are risking pole obstructions but if you use the excellent Precise Seating for Fenway web site you can drill down on specific seats to see if you will have a pole obsruction. Keep in mind that the pole obstructions noted on that site is for baseball so you will have to make an educated guess as the concert stage is set up in deep center field in front of bleacher sections 34-36. With the location of the stage right field boxes and grandstand are closest to the stage. In right field don't go further right than Field Box 6 or 7, or Loge Box 94 as anything toward the right field corner has a bad angle to the stage.
