I would be in seventh heaven if I could procure a rack unit which had the following specs (on each channel):
Insert input: typical unbalanced insert cable (TRS, Tip = Send, Return = Ring)
Output 1: Balanced or unbalanced channel send
Output 2: Balanced or unbalanced sum output
Input 1: Balanced or unbalanced channel return
Input 2: Balanced or unbalanced 2nd signal (such as group, aux, or main output from another mixer). If no cable is inserted, defaults to the send signal.
In addition to converting the typical unbalanced send/return from a typical mixer to a balanced send/return, it would support summing a second signal, on a channel-by-channel basis, either with the send (so that two console groups can be mixed before sending to EFX) or with the return, to support blending of wet/dry signals within the group structure.
Does anybody make such a box? I would love to get a 16-channel version of such a beast fitting a 1U box. This would enable me to link 8 groups, a stereo bus, a solo bus, and link 4 aux sends between two 8-bus consoles. Cool? You bet!