Hi nautec,
Whether or not a 7.1 system sounds better than a 5.1 system is quite room-dependent. In larger rooms, the additional rear channels definitely supply a greater sense of immersion and better coverage over a wider area, particularly for listeners who may be seated at locations off-axis from the main surrounds.
The surrounds in a 5.1 system should ideally be on the side walls, roughly even with or slightly behind the main seating area, and from 2 to 5 feet above ear level when you are seated. The additional two channels for 7.1 are intended to be placed on the wall behind the listening area at the same height as the main surrounds.
Regards,
