My surround speaker are 8 ohms front speaker are 6 ohms the amp is set to 6 ohms What is the impact on surround speaker?

The speaker will be fine and there will be little impact on its performance.

In these situations, if there is a problem, it will be with the amp because that is what delivers the electrical current to the speaker.

The situation you want to avoid is having speakers with a lower impedance connected to your amplifier. So you might have had a problem if your surround speakers were 4 ohms. However, as they have a higher impedance than the amp is set for, I wouldn't worry about it.