I ‘second’ that opinion, in part because the world has moved on so dramatically since 2006 that virtually the whole range of options has changed.
But JosephT’s question about (I presume) Peter Thorne circuits ought to be answered here, if anyone knows.
A tentative answer would be simply to take the output signal, isolate it if necessary, and run it through a commercial sound amplifier to a better speaker. This ought to be easy even with a cheap ‘boombox’ that has a line in, assuming you understand or read up on adapting inputs and outputs to audio equipment…