@Shayne (sorry for the @OP reference previously), where the volume knob is set on your new Emotiva rig means nothing really. What does matter is that you don't run out of volume knob before you reach the sound pressure level that you desire.
What @SD was eluding to earlier is that it takes twice as much power to increase sound pressure level +3 dB. For example, your Magnepan 1.6s are 86 dB efficient (assuming this is 1watt/1meter measured), which means:
1 watt = 86 dB sound pressure level
2 watt = 89 dB
4 watt = 92 dB
8 watt = 95 dB
16 watt = 98 dB
32 watt = 101 dB
64 watt = 104 dB
128 watt = 107 dB
256 watt = 110 dB
512 watt = 113 dB
However, the link below says the 86 dB efficiency rating is not at one watt, but rather 2.83 watts, which means the sound pressure scale above is overstated and your speakers would top out at about 106 dB at 300 WPC RMS, the XPA-2 amp rating.
http://www.magnepan.com/review_MG16_by_Johnathan_Valin