Agreed, it sounds like you could make do with a simple 4-in-1 adapter, or two.
(Though I’m not sure if you already had one 4-slot AMS, and now have 2? Nice score BTW!)
The adapters are passive. They get up to 4 PTFE tubes on the input side, coming from the various sources (AMS/HT/spool/etc), and there’s one output tube to the printer. When an AMS, or you, retract a filament, that automatically frees up the output end for the next filament (input). Which is then simply pushed through as usual. None of the components need to be aware that the adapter is even there. Each adapter can only serve a single hotend.
A switcher device, either manual or the new BL automated one, actively moves input(s) to different output(s). For example to use one AMS unit with multiple printers (not simultaneously), or to change which hotend an AMS/spool is effectively connected to (which can be automated with the new track switch device).
BL sells two versions of their 4-in-1. The newer “H2 series” style has some extra filament wiper pad things… opinions seem to vary on which works “best” but I’ve personally only used the newer style, and only briefly at that (no issues though). (And I have to add/concur that a lot of the MW models are inferior for various reasons.)
My H2C came with one included by default (back in December, anyway).
This guide may help overall, if you haven’t seen it yet (it does not/yet mention the track switcher at all, just the adapters): Connection Guide for Multiple AMS Units with Different Printer Models | Bambu Lab Wiki
So if I understand the desired setup correctly, you’d want two 4-in-1 adapters. Each gets 3 inputs – from AMS, HT, and an external spool holder. Each has one output to a filament input buffer connector on the back of the H2(C|D).
And for soft TPU or those brittle engineering filaments, the buffered inputs are bypassed entirely anyway, so all that setup can be left intact.
Doesn’t seem like the new track switch would have any benefit in this case, though it’s a bit of a boggle to consider all the possibilities. There’s a nice (longish) breakdown posted here, which I found helpful (again, in case you haven’t seen it yet): Usefulness of the Filament Track Switch for the H2C/D
HTH,
-Max