But there is no good reason to put an output transformer on a "good" solid state amplifier, it can only make it’s performance worse.
If 'performance' means THD numbers then yeah I would agree. However if 'performance' means SQ then I can think of a good reason - you want to drive a lower impedance speaker than the amp is designed for. Another good reason is that you have a much higher power amp than you need - the trafo will improve the dynamics in such an instance. If you don't believe me George you could ask Nige at DIYA he's built a battery-fed LM3886 amp with multi-tapped transformers on the output - they are part of the volume control.