vauluck,
I think the Harman Kardon AVP1A processor is just a re-branded version of the Fosgate Audionics Model3A. HK took over the Audionics line some years ago. Here's a link for theAVP1A, look thru it to make sure it's the same as your Fosgate Audionics Model3:
s://www.manualslib.com/manual/65679/Harman-Kardon-Avp1a.html
Just click on page 1 of the thumbnail images along the top of the page and you can scroll through the entire manual.