Benny,
The output offset on the AKSA amplifier is controlled primarily by the mains voltage. It moves up and down considerably, from about -30mV through to +30mV, depending on how accurately it's been set up originally.
The output offset on a modern dynamic speaker has no effect on the sound at all until it gets to about half a volt. Anything under this, particularly up to about 100mV, has no effect at all on the sonics. Believe me, I've tried all this.
Mains voltage is up and down like a yoyo because the mains grid has some VERY BIG current demands. In Australia it can be as low as 232V and as high as 254V, as measured at my home supply. In the States, and other countries using 120V distribution, it probably varies from about 112V to about 128V. That's a big variation and it will affect the offset.
So, don't be too concerned about this; in the scheme of things it is not important.
Cheers,
Hugh