So in reality I know that there's tons of combinations that will work, however seems like most people have a specific set of goals and how it performs in those areas comes down to planning.

So my priorities are simple:

1.) absolute best performance at the lowest buffer with a very large track count.
(I'm aware that usb/thunderbolt can perform *close* but I don't want close - I want the best I can get for this particular facet of performance regardless of the convenience/tradeoffs I sacrifice)

2.) high end converters for end of chain monitoring.
I've been looking at the adi 2/4 se for this very purpose(bonus that it comes with 2 combo inputs)

3.) ability to add atleast ONE expansion of inputs. Ideally one day this'll be higher end, but probably something like the pulse 16 simply to use totalmix to turn it into a bunch of fx loops. I've only a need for a few microphones, I don't plan on recording analog drums again.

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scenario one
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hdspe aio pro
aes into adi 2/4 SE feeding my hs8's(or whatever I eventually choose to replace them with!)
an 8 I/O adat of somekind

from what I understand, the newer AIO pro is supposed to be even faster latency round trip? This should check number 1 box the best and satisfy number 2 while taking a fair hit the expandability with number 3, although this is the lowest priority it's not a deal breaker at that point.

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scenario two
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hdspe raydat
aes into adi 2/4 SE feeding my hs8s
an 8 I/O adat of somekind

this from what I understand has slightly worse(but still nearly best in class) round trip latency but the trade off is significantly more expandability.

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scenario three
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hdspe madi fx
aes into adi 2/4 feeding my hs8s
madi out to something like the pulse 16, then expanding using that ADAT

this again sounds like I lose a little out of number 1(round trip latency), is significantly more expensive - but comes at the added bonus of having FX internally with nearly no latency added.

Much appreciate the advice. I saw somewhere that the converters in the AIO PRO were also as good as the ones on the ADI 2/4 but I'm not sure how this pans out - would I just get an XLR breakout cable to hook them into my HS8s? And at that rate is this truly going to be as high quality monitoring as the fancy ADI 2/4 SE?

other questions people might ask:
I plan on using 48k pretty much exclusively.
I'm working on an 8+ computer setup at the moment hosting virtual instruments in VEPRO, transporting ~128 stereo outs per machine over ethernet. I'm working on solutions to bring the latency down on all of these but there will be very few actual plugins in my DAW as they are processed mostly before my DAW ever sees them.
The instruments I would be hooking up would be my guitar/bass/mic as well pedals/kemper and playing VDrums(superior drummer)

Currently I use a studiocapture - which the power button to turn it on barely works, and the drivers aren't anything to be proud of.   I struggle getting the buffer down before it breaks up.

My current setup consists of a bunch of r9 5950x's, running off m.2 ssds.