yea, it sounds like you've done a lot. Though with unpnp if it works the way it does you shouldn't need to forward the ports. um, speaking of which, which section on the router were you doing the port fowarding? Under port fowarding or under virtual server? If the former, then try first disable the port forwarding, make sure dmz is off, just for a test, disable unpnp, then foward the ports under virtual server if you have not already done so.
with h/w A2, which is what I have, I don't have to touch a thing, no forwarding, no dmz. UnPnP seems to work the way it's supposed to. as well, just revoke the reserved ip address and then do the network setup on the xbox again, wiping out all network settings and try it again. Other than that, I would see if you can RMA the device for an A2 or something because really, i have had very minimal problems all around with A2.