The lower the load to the amp, the lower it's damping factor and the worse the sound gets. The damping factor is a number that shows how well the amp can keep the sub 'under control'.
A 0.8 ohm load is rather low and sound will suffer.
Try with 1 sub (2ohm). Chances are that the sound will be much better and nearly just as 'loud'. The 1100D doesn't double its output when the load impedance is decreased from 2 ohms to 1 ohm. I don't think there will be a lot of difference in sound output.