The nvelope 500 really gets the best out of the two rack slots it sits in. It can be two channels of Full Range or Dual Band impulse shaper or shelving EQ, which can be operated stereo linked or dual mono.
But, the two separate channels can also be used for different tasks at the same time. For example, you can shape one signal in Dual Band mode in channel L and a completely different signal in Full Range mode in channel R.
Or, you can connect the output of channel L to the input of channel R, and then process the frequency response of one single signal with the EQ first, followed by some nice Dual Band impulse shaping.
As you can imagine, there are lots of possible combinations...