Hi Shaun,
Maybe you've already checked that but, just in case...
There's an input meter and a knob to adjust the incoming signal on the upper left-hand side of POD Farm's GUI, just above the gate section. If for some reason that knob is turned too low, you'd typically get a processed signal that doesn't sound as distorted or overdriven as you'd expect.
Sometimes it doesn't look like it's turned down all that much but, for example, if that knob is at 12 o'clock, you're effectively trimming 12 db's off your signal. Enough to make a patch sound weak. On the picture below as you see, my input gain is at 0 - no boost, no cut.
You may also want to make sure that the noise gate isn't set up so that it eats away your signal. Again, you may have already checked that, but it's worth mentioning.
That's the first thing I'd check.
As for impulses... These are meant to be used in conjunction w/ an amp sim. The impulses themselves are like snapshots of speaker and cabinets. You still need to feed them w/ something that sounds like an amplified signal.
Typically, you'd place an amp sim like Pod Farm or Amplitube or Guitar Rig before the impulse loader and disable the cabinet emulation in the amp sim.
Let me know if that helps. :)