I assume since it's your second you know how to care for them as far as acclimation and not exposing to air. With 120 lbs of lr
in a 75 gal
you have a good tank for them. IMO
I wouldn't give up completely, it could have just been ill when you purchased them.
IME if you give Sea Stars very long 3-4 hour drip acclimations and don't expose to air they are usually very hardy and can forage from the sand/lr
with very little additional feedings. (I feed mine a finger nail sized piece of raw shrimp soaked in Selcon once every other week)
I understand if you don't want to try again, it can be very depressing when stock dies and you do everything right.
Out of curiosity could you post your latest water parameter numbers i.e. ph/temp/sg
just to make sure it isn't anything else.