That would seem to describe a digital hybrid type amplifier, in which tubes perform some function, and then the signal is forwarded to a class-D power output stage which then provides audio power amplification to the speaker. There seems to be limited sonic zen in this method, as many have discovered, possibly because the "transfer function" of the tubes is buffered and almost if not totally removed / insulated / distanced / obscured / overpowered by the class-D power amplification, and so what the speaker actually "sees" (or "hears", rather) and responds to is in fact largely or completely the transfer function of the class-D audio power amplification.
In GAGA, however, the power tubes perform 100% of the audio power amplification in linear, push-pull manner WHILE the patented ZOTL impedance converter bidirectionally transfers that power (without losses or limitations normal to traditional audio frequency magnetics) between the low impedance of speakers and the high impedance of the power tubes. Some magic in GAGA is that the necessary impedance conversion that otherwise must be performed by a bulk of iron is now instead performed in a (measurably) nearly perfect manner: Masking by the audio output transformer is eliminated, essentially unleashing the true performance of the power tubes.
Most persons have never played power tubes this way, without audio output transformers; it is exquisite and exhilarating.
Were ZOTL merely some pre-existent technology then it would not have been granted patent. And if it had been erroneously granted patent without technical merit then it would not sustain scrutiny. In fact, ZOTL was patented and remains patented because it is something genuinely unique. Attempting to describe ZOTL in old terms and old paradigms is confusing - which is why it has a new name and why there are sometimes honest misunderstandings.
Ultimately, it's the tone and feel and emotion that matter most, not any particular technique of achieving or amplifying it. After all, many great-sounding amps employ semiconductors (GAGA employs some in new places), and had the digital hybrid scheme of 'tubes buffered by class-D power amplification' actually sounded 'great enough' then anything after would have likely been obviated. Feedback from musicians who play GAGA includes praise for clarity, richness, faithfulness, purity, impact, dimensionality, depth, speed, musicality.
The 1972 AES paper
"Tubes vs. Transistors - Is There An Audible Difference?" shows that tubes used in amplifiers seem to matter most at the input and output stages. GAGA of course uses tubes at the input/preamp stages, and ZOTL in GAGA practically perfectly connects power tubes at the output stage, including the crucial bidirectional conversion of impedance between power tubes and speaker.
