One more question to the calculated numbers.
The O2 is limited at ~200mA so the max. power it should be able to output at 14,4V is 2,88W into 72 Ohm.
At 200mA and 12V the amp should in my theory output 2,4W into 60 Ohm and 1,28W into 32 Ohm at 6,4V.
Even at only 150mA the amp should output 1,35W...