auswalk,
I think Mike's recommendations may be a little ambiguous (either that, or I disagree with some of them). You should turn off ALG and SPI (SPI is a feature of firewall; I think that's what he means by Firewall/SPI). I don't think you should turn off firewall on the router altogether.

Normally, you don't need to put adapter in DMZ, nor forward any ports. Adapter should work just like your softphone - register and forget it. Usually, you enable port forwarding for troubleshooting purposes (such as one-way audio, etc.).

And usually consumer routers notify you that DMZ and port forwarding are conflicting settings; so you really do one or another.

Last, assuming you have Voipo-provided locked adapter, you can't set up STUN server yourself.