Re: 8 ohm amp into a 16 ohm cab...is it safe?
The BBQ grill models that are made in china (metal grill versions) run into 8 ohms, but the AD120VTH head will accomodate 4-16 ohms with no problem. Running the ohm rating differently won't sound all that good. It won't be the worst thing you've ever heard, but it will be pretty muddy and indistinct. Unplug one of the speakers temporarily to get the ohm rating right if you aren't getting the head. It will sound a tad weaker that way, but it will suffice until you get the speaker/cab situation straightened out.
Buy the head version from Guitar Center for $399. That way you can run it just fine with the speakers you currently have.