Superior requires you to “Equip a superior item in every slot with a minimum item level of 187”. However, it doesn’t require you to equip them all at the same time.
If you have one trinket with a level below 187, and the rest of your gear is 187 or above, you can simply swap your 187+ trinket into the other slot to get the achievement.
I tested this with my trinkets, but it should work the same for dual wield weapons and rings.
The Superior achievement has been bugging me for a while, because the Futuresight Rune has much better stats for Resto Druids than a lot of the 187+ trinkets. (I’m after Spirit, MP5 or Spellpower above Haste, so I’m not that impressed by the idea of spending badges on the Egg of Mortal Essence).