Operational amplifier output buffer
If you look at the data sheets for the transistors used you will see that there will be roughly 0.7 volts dropped across Q5 in saturation, 0.367 volts dropped across the 1 Ω emitter resistors and about 0.7 volts dropped across the base-emitter regions of Q1, Q7 and Q9: -

This roughly tells me that with a positive supply of 17 volts, the maximum peak positive voltage on the output into a 13 Ω load is going to be about 15.23 volts.
To get a higher peak output voltage requires either a fundamental change in the way your output stage is wired OR using bootstrap circuits but, bootstrap circuits will only work well when there is an AC content to your signal.
Alternatively, you could use DC-to-DC converters to raise the driver voltage supply 1.5 to 2 volts above the positive rail and 1.5 to 2 volts below the negative rail.