How to select cubes that are behind other cubes

Let's say you've designed a great layout with cubes in several Z-depths with a row in the front and a row in the back and suddenly you decide you want to edit and select a bunch of cubes in the back row.   

How do you do this?

There are two rows of cubes.  (These cubes are transparent in this example.) Make sure you are in Edit mode. Click the rotate left button highlighted in red.

This rotates the view clockwise to the left so it looks like this.

Click on a non-cube area and then drag over the last row which is now on the left.  

Alternatively, if you just want to edit a single cube, you can press the TAB key to cycle through the cubes until you get to the one you want.

Here is more help on editing: http://aeromidi.net/support_manual/cubes.htm 

Hope this helps!