Vandersteen Sub & Adcom Processor Debugging

I just bought a used Vandersteen V2W sub via Audiogon and am having trouble getting it working with an Adcom GTP-880 pre-processor.

Here's what I've tried:

* running the Sub Output to both of the phased inputs (one at a time)
* Plugging the sub directly into the wall & into a Monster 3600 Power Switch

When I plug the sub in, I get a pop so I know the amp is coming on. When I run a test signal, I barely get any noise out of the sub, even when I turn it's gain control all the way up to 15dB and the processor's up to 10dB (both max settings).

I don't seem to be able to get any noticeable sound out of the sub on CDs/DVDs or TV.

I'm using a Monster sub cable which doesn't have a seperate ground which Vandersteen suggests, but I find hard to believe that accounts for no sound. I did swap the sub cable in as an interconnect to one of my front channels and it works fine, so I think I can safely rule out a bad cable.

Any suggestions on how to narrow it down to either the sub or the processor? Is it safe to hook the sub input up to a front output, which I know works, to verify the sub functions?

The processor was a B-Stock purchase & this is the first sub I've attempted to hook up to it, so I have no guarantees the processor's "Sub" output is definitely good. I have turned the Sub ON in the Adcom setup and am running large Fronts (Vandy 2CEs). I currently don't have surrounds/center, but have turned them on to give non-stereo input choices to ensure the sub should be operational.

Thanks for any suggestions, as the lack of bass is quite a disappointment so far.