Isn't nominal impedance of your speakers 3 ohm? It will appear for each amp as 1.5ohm load assuming best case of flat impedance curve. It might trigger protection since your amp is rated at 2ohms minimum load. Better try if it works for one channel before buying another DR9. Play loud heavy orchestral piece for 30min to check if thermal protection doesn't kick in. Few people reported it happening just after 5 minutes (googled for DR9 and "Bridged").
