Lightningboy
Experienced
Just to add. As Yek said, there is a lot more volume from that 2 o'clock position through to full.
Not sure why you are using parallel mode on the amp. That is designed to take a single input signal and split it between two cabs. If you have two inputs plugged in to the amp, the amp will only amplify one anyway.
If you have stereo presets you may run foul of some phasing issue which may hamper volume also.
For a mono cab, just use the amp set to stereo (which effectively splits the amp to two mono amps) and run from one channel.
As far as overloading the cab. Keep an eye on the signal lights on the front of the amp. If it's a newer amp, these are green (older ones pink). They'll start to flicker and stay solid and will give an indication of how much the amp is dishing out. If they are just flickering on an 8 ohm load, you'll be putting out only around 40w. You'll probably find rehearsal and gigging levels between 60-80w (depending how loud you are as a band) so those lights will probably just start staying solid and flicker when you get to the right volume. If you are not seeing any lights and it's loud enough then fine. If you are at full on the amp and the lights are only just starting to flicker or stay solid then an increase in the signal to the amp is required.
Not sure why you are using parallel mode on the amp. That is designed to take a single input signal and split it between two cabs. If you have two inputs plugged in to the amp, the amp will only amplify one anyway.
If you have stereo presets you may run foul of some phasing issue which may hamper volume also.
For a mono cab, just use the amp set to stereo (which effectively splits the amp to two mono amps) and run from one channel.
As far as overloading the cab. Keep an eye on the signal lights on the front of the amp. If it's a newer amp, these are green (older ones pink). They'll start to flicker and stay solid and will give an indication of how much the amp is dishing out. If they are just flickering on an 8 ohm load, you'll be putting out only around 40w. You'll probably find rehearsal and gigging levels between 60-80w (depending how loud you are as a band) so those lights will probably just start staying solid and flicker when you get to the right volume. If you are not seeing any lights and it's loud enough then fine. If you are at full on the amp and the lights are only just starting to flicker or stay solid then an increase in the signal to the amp is required.