The output transformer on the 2nd schematic of the previous post is a 1 to 1 bifilar

 At your risk.

Perhaps it should be possible to use step up output transformers on both Darlington or MOSFET amplifiers so that primary is of lower impedance with a few turns of thick wire. 

In this way the 8 ohms impedance of a speaker would be converted to say 2 ohms or less and power output would be higher at the expense of course of higher power consumption.