I see there's a power amplifier in the Elgar not too dissimilar to a hifi amp. The principal is the same, question the reliability mainly but if you don't overload things too much, they should last a long time. plus you have isolation. Some brainstorming.
A typical AVR of even modest power or an old 2CH amplifier has very low distortion characteristics. They are 2nd hand very inexpensive. If you want to make a clean supply with low distortion, a precision sine wave generator that outputs 0.775V fed into an amplifier. Use the low output impedance of the speaker terminals in mono bridge mode into a step up transformer to 120V or 60-0-60 (240, 120-0-120 for EU). You would have to add protection, GFCI/RCD of course. The amplifiers have good protection circuitry. The voltage will vary, but nothing most modern electronics can cope with easily.
Depending on the size of your amplifier, even a modest 100W would be achievable, enough to drive a computer, DAC, tuner and it would be reasonably quiet.
A sine wave generator can be a wave file played in a continuous loop on an old clunker PC.
