I would recommend getting a 4 channel amp for the best sound and best longevity. If your set on keeping the 2 channel amp, you can run and other set of 2 ohm speakers in series, or run 4 ,4ohm speakers in parallel . Using the last two options, you'll lose total power output to each speaker.
I believe JM will give you a discount if you upgrade their equipment and send the old back in. Give John a shout on this.