No no, I never said Mixed armour trumps Torrent of fire. The two are perfectly compatible IMO, and MA rules don't specify that ToF is overruled.
But, it fairly obviously will trump page 27.
MA rules pg 76 say the normal casualty removal and armour save rules are modified, as per the text that immediately follows.
You follow the MA rules always for MA units. And, once you've rolled, say, your 5+ saves, and failed however many, they can't be applied to a 3+ save creature - Unsaved wounding hits must be applied against models with the same armour type that was used for the save'.
Note the pg 27 rule contains the amendment '...where possible'. This would be one of those times where it is not possible to follow the rule.