I should relate one bit of advice when running multiple Guitar Amps in a large room / concert hall.
If you do not manage the acoustic phase cancellation that physically occurs due to multiple Non Time Aligned Audio Point Sources (i.e. Multiple Guitar Amps spread across a large stage in a Large Concert Venue) , you may find the audience will report that your Live tone sucks compared to the opening Acts Guitarist who only used one 1965 Fender Deluxe Reverb close mic'ed with one Shure SM57.
More technical discussion on Audio Time alignment is herehttp://sound.westhost.com/ptd.htm
True, Many classic Guitar tones we all know (Brian May) are the result of Multiple Guitar Amps with CAREFULLY PLACED Microphones located both near the Amp's Guitar Speaker and far away which creates phase errors in a controlled studio environment, This creates a resonant peal thick tone due to phase errors -and its important the resulting dominant resonant tone frequency does not conflict with the key of the song - so it often handy to have the same tools / knowledge to tune your Live rig for the specific venue, key of song, guitar type used - all play a factor in distant mic placement.
Typically The recording Producer listens to the combined "mix" of all sources for the guitar being recorded (DI Box, DSP Modeler direct out, room mics, etc) - and instructs the recording engineer to move the room microphones until it sounds good with the current song being produced. There are no hard and fast rules, and often its takes several pages and days of math analysis for a PhD to explain in full scientific detail the same "audio phase error "phenomena that a producer / engineer with good ears can set up with multiple mics in seconds for the benefit of the song and delivering "thicker sound" for the guitars.
I suggest get a set of good closed headphones - like Audio Technica ATH-M50Shttp://www.amazon.com/gp/product/B004ZG9TMA/ref=oh_details_o08_s00_i00?ie=UTF8&psc=1
and have a friend play guitar, while another friend moves a few mics to separate locations (near and far from amp) in a separate room and record all elements on separate tracks and mixed to mono for analysis / playback review.
DO this for a day or two and you should have better first hand knowledge of phase errors due to multiple point sources
On the cheap, one method is use a Yamaha 01V Mixer as a Guitar "Pre-mixer" - before your FOH Board feed.http://www.soundonsound.com/sos/jul98/articles/yam01v.html
Each night, be sure all your Guitar Cab mics are consistent: set at the exact same distance / position relative to the speaker.
Run every guitar amp mic into a separate channel on the 01V , then employ the individual "Channel Delay" controls (with its 0.1 millisecond resolution) on each channel of the Yamaha Mixer to assist with restoring time alignment and minimize the Phase cancellation for all the guitar amps in that specific room.
I see band Riders for touring bands , and many do specify "Yamaha Mixer Only" - for this specific reason, because bulk of Mixers lack the unique Channel Delay controls
that are built into most high end Yamaha Digital Mixers.
But know that most Professionals who are reading here understand all that - been there, done that, bought the T-Shirt.
and in 2013 many major acts have opted / or have tours managers who insist the whole band USE no onstage guitar amps, and In Ear Monitors for the whole band with better management of all stage audio sources to allow the FOH Mixer more complete control over the bands Live sound.
The biggest complaint most FOH Mixers inform is lack of ability to "Turn Down the Guitar" when confronted with acts with guitarists with large multi-amp rigs.
I also recommend buy PlexiGlass Shields to place in front of the guitar cabs, to assist your FOH Mixer's job, and improve the audiences's opinion of your live act, and sell more CD's.http://www.thegearpage.net/board/showthread.php?t=1055062