I have a Problem with my K4000. The Speakersignal is to low.

Is it posible, that both Out-Transformators are demaged?

I also have only 5,7V and not the 6,3V I have to have. Is this to low?

We are afraid that such a vague complaint does not allow us to determine the cause of troubles. Measure all HT voltages and compare with manual.
Check complete assembly. Is the 5.7V measured at full load or no load ?
Please provide as many details as possible.