SRAM and Quarq power meter spiders are typically paired with DUB crank arms and a SRAM DUB bottom bracket. This is SRAM’s newest interface and is the one we recommend for most frames. However, SRAM doesn’t offer a DUB bottom bracket for Trek BB90 bikes.
So if you have a Trek BB90, you have two options for a SRAM or Quarq power meter:
1) Purchase a DUB bottom bracket from companies like Kogel or CeramicSpeed.
2) Purchase a set of SRAM RED GXP Crank Arms or SRAM Force GXP Crank Arms to use with your Quarq power meter. The GXP cranks would fit your Trek BB90 bike assuming you have or install a compatible bottom bracket.