installing the 3/4 speaker connector involves adding an additional amplifier, the actual speaker connector, signal and power wires.
it is a little involved but it is a simple install though.
this amp is capable of driving a 2 ohm load, you could just add more speakers to the existing amp. it can handle it. they say it's 800 watts at 2 ohms, so could be safe to assume 600 without damage at 2 ohms (300 RMS). just keep a load on the amp between 8 and 2 ohms and you will be fine.
REMEMBER:
series speaker connections, add all the ohms together for total load rating.... parallel speaker connections: take the first speaker ohm rating and divide by 1/2 for each additional speaker.
example: 2 of the same 6 ohm speakers in parallel on one channel: 6/2 = 3ohms adding a third speaker and it drops to 1.5 ohms. (3/2 = 1.5)
example2:3 8 ohm speakers in parallel is 2 ohms. 8/2 = 4 and 4/2 = 2
to double check you can read the line with a volt meter set to resistor check. as actual results from calculations vary due to wire resistance and differences in speaker manufacturing.