Adding an fx send/return to a mixer

[Dyonight]

Hi!

I want to add a mono fx send stereo return to a Presonus hp60 headphone amp:

PreSonus

The fx would affect the aux in only (1 send on each 6 channels) and be mixed back in stereo with the main common out.

Does anyone could give me a basic fx send plan? Sound quality don't have to be pristine and minimal mod and passive design would be preferable.

Thanks for any help!

 

[Dyonight]

I would even add that a simple switch "in 100% wet - out 100% dry" would do the job since I would do the balance with the fx unit. So a 6 channel A/B router to stereo summing and a circuit that mix the fx back...