Well, it's not a budget solution for a rig, but it is extremely versatile, and has a lot of advantages.
You can use the AxeFX as a simple preamp and effects device, like Hogan did, connecting it to a power amp and a conventional guitar cabinet. I have used it like that, and probably will in the future for really big stages where I feel like I want the cabinet to fill the sound out in front.
Or, you can use the AxeFX as preamp, reverb, effects, power amp and speaker cabinet, using a full-range (FR) powered monitor, which is what I am doing most of the time. To that, you need the AxeFX and some kind of powered monitor. I chose the QSC K12; the other "hot" FR monitor is the Verve 12MA, which is coaxial. I tried out a pair, they are nice, but I didn't think they were that much better than the QSC so I passed on them.
The Ground Control Pro (or any other MIDI pedal board device) is useful for changing presets, turning effects on and off on the fly, using expression pedals to control things like volume, wah, phaser rate, delay levels, etc. But it's not necessary to use it.
You don't need to hook it up to a computer to use it, but you do need the computer to update the firmware, back up your presets and load other people's presets. It uses MIDI to communicate with the computer, which requires a MIDI interface for the computer. (This is its biggest flaw, IMHO, it would be much better and less balky to have a USB interface onboard.)
AxeFX: $1499 ($1999 for the Ultra)
QSC K12: $675 street
MIDI interface: $50
GCP: $399 (or a cheap used Behringer or whatever ...)
I have a Garcia-style patch that's set up with all the effects (QTron, Octave, Phase 100, MXR Dist +, wah, delay) and it's configured to use the effects loop on the guitar, just like when I had all those real stompboxes wired up through a GCX. I made impulse response files for my JBL cabinets, which work perfectly.
The AxeFX will work with your Mackies. The question is, how flat and true is the response curve on those speakers? The ideal (which is unobtainable, basically) is to have a perfectly flat monitor so that you can dial in your guitar tone, then send that guitar tone direct to the board where it sounds the same over the perfectly flat PA. In the real world, nothing is perfectly flat. So, what sounds "right" to your ears on your Mackie 350 might be too bassy on your Mackie 450 and could well sound terrible over a high-quality PA. The AxeFX compensates for that, to a degree, by giving you two sets of outputs, with separate 10-band EQs on each one.
I chose the K12 because it's supposed to have a relatively flat response curve. It's worked out well for me, plus it's loud as hell (131 db), relatively light and has a six-year warranty. I can tell you that with the K12 positioned like a vocal wedge, I have never heard myself so well on stage before. I use a second one behind me to fill for the audience right in front, but I don't need it to hear myself. And now, my tone is the same regardless of the venue, acoustics, stage conditions, and so forth. The FOH engineer gets the sound I want to give him, it's not dependent on his cabinet mic, micing techniques, etc.
The icing on the cake, compared to the big just-Jerry rig I used to carry, is I can take this little two-space rack unit and dial in the Garcia tone, but a twist of the knob gives me Carlos' Boogie, Slash's Marshall, Stevie Ray's Vibroverb, Townshend's HiWatt and dozens of other amps and speakers, plus every effect under the sun, from a Rat fuzzbox to a Univibe to the Edge's 10-tap delays to a Whammy to guitar synthesizers to anything you can dream of, plus a vocoder, 16-second looper ... the list goes on. It's a great recording device and a really well thought out live tool. Want to play through a Vox Top Boost into a 2X12 on the right channel and a Marshall Plexi into a 4X12 on the left channel, at the same time, with some delay, reverb, overdrive and chorus on the Top Boost but nothing on the Marshall? Just build a preset for it.
However, there is a fairly steep learning curve to it, so don't expect to master it right out of the box. It's not a Pod. But it doesn't sound like one, either. And if you want to be able to digitally change the value of your brightness capacitor, the bias on your power tubes, the frequency your presence control works on, or add a Fender Brownface tone stack to a Matchless amp, you can do all that when you dig into the deeper parameters on there.
