When I had 2 units in my VW Polo I removed the pins from the stock docking connector one by one and soldered in (carefully) wires from an aftermarket ISO connector to the "throat" part of the pins on the stock connector, and then reinserted the pins into the stock connector. Didn't even need any extra isolation (shrink tubing), as the back of the stock connector was "compartmentalized" (ie provided isolation between pins).

You could do it less hackish by buying an ISO plug and 2 ISO connectors and fashion a Y-connector, ISO style...

Beware that sometimes the stock wiring isn't all that good (though the empeg doesn't draw very much power) and might have problems supplying and/or properly grounding 2 units. Running new wires for power and ground might be a good idea.

You need to decide (or combine using diodes) which HU that turns on your amp and only wire that one up.

/Michael