The AN-X engine in the M models has 3 oscillators and a 4th 'noise' source.

The 3 oscs are mostly identical except osc #3 can provide independent feeds to osc #1 and osc #2 as shown on p.12/13 and p.414 of the operation doc.

Features three Oscillators and one Noise generator.
OSC3 modulates OSC1 and OSC2 (either with frequency modulation or ring modulation)
Each OSC controls the shape of the waves by using Pulse Width, OSC Self Sync, or Wave
Shaper.
You can set each OSC to output before or after Filter 1 and Filter 2.

Although it says 'either with frequency modulation or ring modulation' you can set send levels for both of them. I can't find any indication of an 'either/or' relationship based on limited testing.

The diagram shows that the FM Mod feed is to the INPUT of osc #1 or osc #2 while the Ring Mod feed is to the OUTPUT.

The FM modulation appears to be the same, or similar, to an FM engine modulator/carrier relationship.

But what is the Ring Mod feed actually doing in the context of the M model architecture shown?

Note that the SAME source (osc #3) and signal will be used for both types of modulation.

Question - are there use cases for doing both FM and Ring mod using the SAME signal feed? My personal experience with Ring Mod in particular is that it would be customized to its purpose and that isn't likely to be what would make sense from an FM mod perspective.

Can anyone shed any light on this?

My current thinking is that the design is really to effect that 'EITHER/OR' that was mentioned and give the user flexibility but that it wasn't expected that you would actually use both Ring and FM at the same time. That is, that either Ring Level would be non-zero or FM Level would be non-zero.

That would explain the anomaly I reported in another thread where tweaking the 'Ring <-> Fm' sub display knob actually resets the opposing level to 0 even though the main display knobs allow both levels to be non-zero.

Any thoughts?