Into the board

The XLR (the three conductor plug/jack most often used for balanced, 600 ohm lines with mics and preamp outs) on your Clarus is a built-in DI (Direct Injection) output which can be connected directly to a PA board input. The power of the amp is inconsequential, as the DI is a line out from the preamp, before the power amp. So all you need is a standard XLR male to female cable to go from your Clarus' DI to the PA board input.

Acoustic Image stuff www.bobthebassguy.com/accimg.html

 

The Clarus DI is post-EQ. This means that the first volume control and all the tone controls affect the output signal. You should set them to an agreeable position from your own personal standpoint, so once the sound check is complete you shouldn't touch them again or you will affect the main mix. The master volume control on the Clarus only affects your stage (amplifier) volume, and can be adjusted if your volume needs to be changed.

Unless the band won't have you in the monitors, and/or isn't able to hear you from your current onstage speaker cabinet, I don't think it should be necessary to add a speaker. If, for some reason you're not in the monitors and/or the whole band can't hear you well enough, you could conceivably put a second cabinet on the other side of the stage. However, bass frequencies being mostly omnidirectional, unless the stage volume is really high (better get earplugs!), it probably shouldn't be necessary.

Depending on that situation, and how well you can hear yourself, you may even want to treat your Bag End more like a personal monitor, like tilting it back securely against something, or with an amp stand, putting it up higher on a milk crate, etc.