300 watts would also blow that 70W rated speaker.
No one has mentioned the output section settings which typically involve a pad setting (volume cut - default is 12 dB pad (cut) which is a lot) for the Monitor Out.
It is possible by adjusting this setting to boost the Monitor Out levels considerably (so that they are louder at the same settings on the front volume control) and also to see a meter showing the current power level which is an aid to protecting your speaker from overload.