For Shimano cranks with a clamp on front derailleur, the spacers are:
68mm BB shell - 1 x 2.5mm spacer on the non drive side, 2 x 2.5mm spacers on the drive side
73mm BB shell - No spacer on the non-drive side, 1 x 2.5mm spacer on the drive side.
Shimano Mountain BBs are a little longer in the threaded insert than their road counterparts to allow for the spacers.
Looks like you've tried with various combinations to no avail. Almost like the crank has been made with a road bike crank axle length as opposed to the longer MTB axle.
Sorry to hear it hasn't worked out.
If your heart is set on external BB triples - I have had good luck with Race Face Deus cranks, using Shimano BBs (Race Face ones don't have the longevity in my experience).
Just a note, if you go with a Truvativ crank, they take a different BB to Shimano/Race Face/FSA cranks. Truvativ ones have a narrow crank axle on one side.
Life was simpler when it was square taper or square taper!
Grumps