I have made mine work will take photo's at weekend to show what i have done, as long that your new head unit has sub outs on the back theres a 95% chance that your will work the same as mine, especially how you mention the thud
i took an old aux lead and cut it to 10cm
take the old connectors (to the sub) off and strip wire back, you should have 2 outer wires and 2 inner
strip to 10cm aux lead so that there is 2cm of wire exposed ( again 2 outer 2 inner)
now i this sounds daft but bare with me as you only need to connect one of the 4 wires from the sub to the stripped aux lead to work,
if you connect 2 it cancels it for some unknown reason
i cant remember off top of my head which is the best one to connect from the sub ( and there is a difference) but i will get back with a photo, but in the mean time have a play wi it and you could get working.