Read what others have said about trying to do it in analogue modular Vs digital when you’re aiming to emulate a digital synth.
But anyway, if you’re up for multi operator analogue modular FM (which I am and is cool 
) you should check out the nonlinear circuits FM op and valmorification modules for osc and envelope as this is what they were designed for. Tricky DIY build if you’re up for it, of you can buy built.
As for oscillators you could get away with 6x 2hp sine. Get something like a Bastl waver (2x?) and a stereo filter (ikarie?)
As for envelopes and VCA’s you can’t go wrong with MI Stages and Veils
Unfortunately the built price of this is $250.
Here’s a decent explanation with accompanying video of the different kinds of FM. Understanding the Differences Between Exponential, Linear, and Through Zero FM | Learning Modular
Same here, though the number of modulators and vcas I feel I’d need to properly control it feels a bit overwhelming. Kind of considering selling off some of the analog focused stuff for it though.
I got excited about the FM capabilities Generate 3 + other modules brought, but I actually think I got better overall results from using Plaits, Tides, and Warps together. Cross modulating a bunch of analog vcos, filters and function generators is good fun, but digital FM in modular can be cool too
I said it once, I’ll say it again: Humble Audio Quad Operator. It’s as knobby as you can get.
And the Andrew Huang vid for all the haters:
3 x Frap Tools Brenso and perhaps a Fallistri or two.
Yea, more appealing as DIY if you’re up for it.
Yup. Digital FM is in fact phase modulation. Otherwise it’s impossible to achieve “musicality”. Technically, the idea of 6 op analog fm synth would turn out more like a 3 oscillator drone machine instead of a “playable” instrument.
Here’s a curve ball… Rossum Assimil8or why settle for analog FM when you can have Samples FM/AM/PM
Just to be clear, I’m definitely not trying to achieve an analog perfect digital FM.
Thanks everyone. I hoped to get some quality info and suggestions from the modular boffins around here, and that’s what I got 
I should have realised that VCOs wouldn’t be through zero! I’ll be checking out every module suggested, with the additional knowledge you have given on what does and doesn’t work. It’ll take a few weeks to get modules and check out what’s available locally.
Well, if you do end up buying 6 oscillators and get them oscillating each other, I would imagine it would be fun. Not sure how musical it will be, but honestly with eurorack, musicality is not really the only focus. I have a DPO, Tides and Tiptop 258t…all of which can modulate each other, and that’s really what modular is about. I could suggest Mutable Instruments Tides as something to look into. It can be used as an oscillator or modulator… But as many have suggested, building a traditional (traditional anything really) 6 op FM synth with modular may be a fools errand. But, it’s whatever really, because you will probably end up with something even better just by the nature of the beast.
Check:
Beautiful sounding module for super cheap.
Actually was suggested to me a few weeks ago, but they couldn’t get stock at that time (Polish/Russian relations?).
I’ll follow up today!
Looks like all the colors are in stock at Detroit Modular - which is where I got my Lyra & Syntrx last year.
Last I heard was that manufacturing for non-RU orders happens in Poland, and they recently opened a US distribution office.