If I understand your setup correctly, then mine compares like this:
Where you have SIPGate setup, I am using a second VoXBasic Account
Sometimes, it helps to add a # at the end when you are done dialing the number you want through the CallThru
(The other difference is I have been using PBXes rather than a SPA3102)
See:
Placing VoIP Calls from any Old Regular PSTN Phone
Replace putting in various outgoing Providers with just putting in your VoXPremium Account as a Provider (as per that guide)....
It's been working quite nice