Richard, the availability of enough room(say at least 4')behind the listening position for a rear sound field to form is significant re the back surround speaker question. As to available information, note that using a mode such as DPLIIx can send useful signals there from both 2 and 5 channel source materials.
On the back vs front question, Dean(grunt)is our member with the most experience in this area and hopefully he'll see this thread. From his past comments it appears that although he finds both back surrounds and front heights of benefit on occasion, he has the highest satisfaction with using the Audyssey DSX processing(with 5.1 source material)for front width speakers.
