Inverting a signal means that what was positive before now becomes negative, and vice versa. Some circuits invert the signal, and some don't.
Some say that getting the correct phase of the signal from your speaker is important. That is, since the initial transient of a drum compressed the air, then so should your speaker on that initial transient.
So, some think that your system should preserve phase from the recording to the speaker. I think this is a bit silly for two reasons. First, you don't know if the recording is in or out of phase. Second, you can reverse the phase easily enough by swapping the leads to the speakers. Finally, most (not all) crossovers tend to smear the phase across the audio band anyway.
If you really want to be able to get the absolute phase correct, then you need a preamp with a phase invert switch. Otherwise, don't worry is my advice
JohnR
