I believe you have it understood. Load up a virtual instrument, and it should play back through the Firepod as audio, as long as you choose that as the output in the track.
If you have a small mixer, you could run the Firepod outputs to it, and also the MIDI soundcard outputs, and then run the amp/speakers/headphones out of that.
That way you could at least use the MIDI from your MIDI soundcard as a guide while working.
When I start a MIDI sequence, I use only one soundcard, the GM set, and do it as simply as possible....just to get the performance notes and arrangement down. Once the arrangement is done linearly (tempo changes, verses, choruses, etc,..finished), then I start worrying about finding sounds.
Obsessing with the sound quality WHILE I am composing obstructs the flow of creation. That's the left-brain/right-brain thing. Construct the framework before you start adding paint. I do, however, do quick pans and volume edits to tracks....just to keep everything under control and out of the middle.
Once I have it at the tempo I want, and the basic instrumentation chosen...I then start looking for sounds that compliment each other. It might be a sound out of my old Roland RAP-10 card or a SoundFont out of my Audigy on my old MIDI computer. Since I have it synced to my audio computer, I copy the basic MIDI track to it, and I can choose use a different sound out of its Audigy, or use a virtual instrument.
I may start copying tracks so that I can assign the same track performance to a different sound. Maybe I like the sound of the RAP-10 Slap Bass mixed with a SoundFont Finger Bass, and I might even copy the track again and assign it to a virtual bass. These are all running through my Mackie, so I can hear it all. With some careful editing on velocities and volumes, I can make the bass more "alive" by having the Slap Bass pop out only when I need it.
I may do the same with drums. Use three different Crash Cymbals...all the same performance...and playing around with velocities. Sometimes I'll just "randomize" the velocities a bit. That makes it sound like the stick is maybe hitting the crash closer to the edge sometimes, and closer to the center sometimes. Keeps it from sounding quite so static and "MIDI"ey.
I may do a left string section, and a right string section. I can go crazy with strings! Start doubling and tripling up different string patches, and it's instant lush. May even transpose something up or down an octave...if it needs it. I've even taken a right string section, copy it, move it to the left with a different patch, delay it a tiny bit, and slide it under the left strings so that it doesn't compete, but you know it's there. Makes it sound like they are reverberating a bit in a hall. Do the same thing with the opposite...stereo heaven.
I have a few keyboards and outboard modules that I also employ into service....if I want those sounds. when I think I'm done choosing sounds...the hard part comes. Getting those sounds from soundcards, modules, keyboards and such out of them, and into audio.
Sometimes, I'll just let them all run through the Mackie, and premix to stereo....recording say, all the string section to stereo audio, while all the other tracks are muted. Start over, premix the basses. Start over, and do the drums. The drums are a bit different. I may premix all the toms alone, hats alone, cymbals alone, snares alone, and the kicks alone premixed with themselves down to their own stereo tracks so I can adjust those seperately in the mix. Maybe I want the kicks dry, but I want a certain reverb on the snares and cymbals. I do all that, and then I mix it ALL down to stereo....always keeping the originals in case I need to go back.
Sometimes I'll patch out of each MIDI card, keyboard or module seperately, and record them directly to their own track through the Delta 1010's eight inputs...all at once...bypassing the mixer.
Eventually, I may have 40-50 MIDI tracks mixed down to 12...15...whatever...stereo audio tracks. I can then mix those with whatever actual real-instrument audio I have recorded.
BTW, I usually record guitars, bass, perhaps Hammond, and vocals as audio along with the basic MIDI tracks early on. The audio computer is Master, and the old MIDI computer is synced to respond to it. I have to find sounds that fit around the actual audio, not the other way around. It's more destructive to tamper with audio tracks, than it is to find a different MIDI patch, or to tweak a patch's tuning, filter, EQ, etc.
Now then. There are free or cheap applications available that will let you play SoundFonts through many soundcards, and probably through your Firepod.(Google "SoundFont players" or similar). Using SoundFonts is kind of like having a soundcard with unlimited replaceable banks. Mix'n'match. Tweak the sounds. The drawback to SoundFonts is they are not as interactive as a good virtual instrument. You CAN get them to do some cool stuff with MIDI control info, but it's more work intensive. They also don't use much horsepower from your machine.
Virtual instruments may be more interactive, especially real-time control, but they take more of a toll on your processing power.
There are good and bad of both SoundFonts and virtual instruments. There are THOUSANDS of free Soundfonts, a few decent free virtual instruments. There are commercial sets of both, both inexpensive and REALLY expensive. There are virtual instrument synthesizers, which don't actually use samples, but generate sound much like a keyboard synth. There are virtual instrument drum sets.
So, go ahead and use the crappy MIDI sounds out of your soundcard as a guide track to record your virtuoso guitar performances. The notes are all there...although they may sound crappy for the moment.
Once you have recorded all your glorious audio performances, start finding sounds to replace the crappy MIDI sounds, and that will compliment your carefully recorded guitar and vocals. Dinker with the MIDI...not so much the audio.
Here's a good place to start:
http://www.kvraudio.com/get.php
I think you have the picture. Hope this helped.
HDB