I would rule out the 8.75 as its probably worse off then the one that your trying to cycle right now.
Test the big tank again tomorrow and make sure that you didnt get an error in your testing. Watch the fish, your probably gonna be doing water changes daily for a bit. I dont know much about the crabs but out of the shrimp your amanos are probably the hardiest of the bunch. The NEOs should be fine in the spec 3 for a bit as long as the water parameters are good for now but its not leaving much room for error.
Honestly its hard to recommend what to do as all that stuff in a spec 3 could send it over the edge. In my own opinion I would probably do another water change on big tank tomorrow, test parameters, add the new arrivals like planned, continue monitoring/testing and hope for the best.
Hopefully others will chime in with better ideas and advice.
EDIT: Wanted to add, the spec 3 may be ok with the inverts but gonna have to do water changes and keep an eye on parameters closely. The shrimp should have a small bioload but not sure about the crabs.
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