To the OP if you got your Z-5500 control pod working and you're still interested in hooking up the Z-5500 sub to a receiver it can be done.
You'll need a subwoofer cable (plain RCA can work too but the shielding is sometimes poor) and a 3.5mm male to Female RCA adapter.
Attach the adapter to one end of the subwoofer cable.
Plug the other RCA end into your receiver.
Plug the 3.5mm end into the Center/Sub input on the Z-5500 Control Pod.
Make sure the switch is set to 6ch direct and voila! Subwooferage!
You can then use whatever Auto Calibration software is present on your receiver to set things up.
While the sub may be a few steps below the quality of those from other companies, you already have it. No harm in trying it out before you invest in another one.
As for me, I'd love to upgrade to something better however, being out in the Caribbean I'd be looking at close to twice the cost to get it here.