If you supply the amp with voltage range of 2.5V and 5.5V between V+ & V-, the amp will operate according to the specifications.
If you exceed the 7.5V, the amp could be destroyed (absolute maximum rating). If you apply more than 5.5V and less than 7.5V the amp would work fine; but it's possible that it doesn't meet some of the specifications anymore.
The power supply voltage is always measured between V+ and V-