I have been vicariously following a conversation on the Yahoo Yamaha DX list and figured i should post this for posterity.

List and Breakdown of Yamaha FM Synthesis series chip set and instruments:

4-op:

OPN* (YM2413, YM2608, YM2612, YM3438, YMF278, etc.): used in games consoles, 3 or 6 channels, sine only, sometimes built-in DAC or SSG square wave chip
OPL*: used in SoundBlaster/AdLib-type cards, 4- or 2-op chips that added more waveforms and channels as the lineage descended
YM2151/OPM: 8 channels, sine, used in arcade boards
YM2164/OPP: basically identical to OPM, used in FB-01, DX100, DX21, DX27(S)
YM2414/OPZ: OPM/P + 7 extra waveforms + fixed frequencies + EG effects, used in TX81Z, DX11, TQ5, YS100, YS200
YM2424/OPZII: OPZII + fixed frequencies down to 0 Hz, still only 8 channels as the only synth in which it was used, the V50, obtained its 16 channels by using 2 OPZII chips

6-op:
YM2128(0)/OPS + YM2129(0)/EGS: used in DX7, TX7, and TF1; and in DX9 with its crippled 4-op firmware
YM2604/OPSII + EGM: used in DX7 II/S and TX802
OPS3 + EGM2: used in SY77, TG77, and SY99, clearly an almost exact merger of the OPSII and OPZII but with many new features and, by volume of features, surely the most capable FM chips Yamaha ever made

8-op:
whatever those ones were in the FVX1
the ones in the FS1R, which although having 8 ops, only has 1 feedback loop and simpler envelopes and other drawbacks when compared to the OPS3 in the 77/99

2-op:
OPL* as stipulated above
about a million chips from things like the vector synths, PSRs, etc.

::: IF :::