The TG77 has 6 operators, but their waveform is not only sine. 16 different sine modifications (e.g. absolute sine)are available. As far as I know, the algorithms are the same as in the DX-series.
Besides the FM-synthesis the TG77 also has 16 voices that can playback rom-samples as paino, strigns and so on. But from today´s point of view they sound rather cheap.

You can change every parameter, and believe me, there are much more than in an old DX7.

Shima