Cabinets have rated maximum power they can receive, amplifiers deliver those watts. If you connect a 1 watt amplifier to a 450 watt capable cabinet, it's still only 1 watt of delivered power.
From the RB210 manual
Output power: 500 Watts RMS @ 4 5% THD+N (with external speaker) 250 Watts RMS @ 8 2% THD+N
The extension cabinet should be able to accommodate at least 250 watts RMS. A 150 watt extension cabinet would not be a good match.
From the RB210 manual
Output power: 500 Watts RMS @ 4 5% THD+N (with external speaker) 250 Watts RMS @ 8 2% THD+N
The extension cabinet should be able to accommodate at least 250 watts RMS. A 150 watt extension cabinet would not be a good match.