Line6 Vetta + Rocktron Chameleon: Anyone else try this?

I'm not sure if I've asked a variation of this on here before or not,
but I wanted to run this by the group. Is there anyone here who has a
Line6 Vetta and who is using an offboard/rackmount FX/DSP/preamp box
in the Vetta's effects loop? I can't be the only one doing this, I'm
sure. Anyway, I went to Line6's FAQTRAQ and posted a question there,
we'll see what they say. I'm trying to use the awesome
channels/patches of my Rocktron Chameleon 2000 as a preamp for the
Vetta, the problem is, I have no idea how to set up the Vetta to just
pass the signal from the Chameleon through without 'molesting' it with
all the amps, cabs, FX, etc. on the Vetta. I can't seem to totally
get rid of the amp(s) I have dialed up on the Vetta but I *can* hear
the Rocktron's channel coming through.

As a concrete example of what I'm talking about, for those who are
still reading and whose eyes haven't glazed over yet...

1. Assume the Rocktron is hooked up in the Vetta FX loop (which it
is).
2. Dial up the Jimmy Page channel on the Rocktron.
3. Put some headphones in the back of the Chameleon. Sounds just like
Jimmy! Pretty scary.
4. Now unplug the headphones and put them into the phone jack on the
Vetta. Hmm, doesn't sound the same. Something's not right.

I've d*cked with the Vetta's settings a lot and can't seem to just use
it as a pure power amp. Which leads me to my next question for the
group:

What is the difference between a preamp and a power amp in guitar
terminology?

Okay, that's all for now. Thanks for reading and any responses will
be helpful.

Regards,
Mike