dudes maybe were getting a little ahead of ourselves here; i mean you have the guy spending all that money already when a little judicious tweaking of his current plugins will probably help make his mix "bigger"
im not a working engineer/producer so take this advise with "however many a grains of salt" as you wish 
also i dont know your (original poster) level of experience so, sorry if you know all this already
doubling the guitar parts can make it seem bigger nga but if its the exact same track it can actually make it seem smaller cause of phase cancellation; you can get around this by re-recording the track using slightly different eq settings, mic placement, gain settings. also the impossibility of getting the 2nd take exactly identical to the first will introduce slight variations in pitch/tone/etc which will help the illusion of width
compression can either make or break your track also. too much can squash the dynamics out of your mixes; too little and it could lack in punch. i tend to compress each instruments seperately and then apply a mild limiter over the master. compression is really a tricky thing; its not as obvious as other effects but its definitely the "secret sauce" and youll know if its not there
eq'ing naman: ideally you would like to carve out a sonic space for each of the instruments so that they dont step on/cancel each other out. say you have a deep boomy kik drum, it would help to eq out the kik's dominant frequency out of the bass guitar track, so they coexist together peacefully. that also goes for other instruments that share similar frequency ranges: guitars and keys and voice for example. the idea is hindi sila magtapakan, frequency-wise
reverb can give the illusion of depth but too much can make the instrument blend into the background. i like to eq out the low frequencies from the reverb also to avoid it muddying up the mix.
hope you weren't talking to me because I didn't say the guy should get a distressor, and the suggestions I offered earlier were minimal costing, readily accessible options that do not cost an arm and a leg to invest in. Moreover, as a longtime Audition user (I started back in the day when it was known as Cool Edit), the current lot of Audition plugs as far as compression goes only includes a Multiband compressor which hardly offers any degree of warmth or liveliness even if you use ducking in the mixing of the tracks.
if you double a track, it shouldn't be an identical track as this defeats the purpose of doubling a track which aims to layer sounds in the first place. in a tracking situation, you double a track to give it depth by playing the part the same way through a different amp or guitar to give it a dimensional character, OR you EQ it differently (using a different shelving EQ value) to bring out, say, its attack, relative to the original recorded track. In both cases, you layer both sounds but keep the signal mono in the eventual mixdown by sending the mix to a subgroup on your mixer. Here, you can make a very big difference in the process of layering to make a solid, main, track and you can supplement the "width" of your guitar sound by duplicating the track and panning it to the opposite side of the stereo field BUT backing the volume down on the duplicate to give the illusion of a stereo signal. This is an old Brian Eno trick that is quite rampant on U2 records to give The Edge's guitars that "larger than life" sound.
as far as compression goes, application depends on the genre and goal of the track. by default, I apply slight compression to drums and bass, leaving compression off vocals and guitars until I am convinced that there is absolutely a need for it in the context of the song.
EQ'ing should be done according to the frequency responses appropriate for each instrument. there are specific red book values for all the intruments and you can use something like a spectral analyzer to see if your EQ adjustments are on pat after you mix a song.
experiment and see how compression affects your sound. with the variety of monitoring systems, it is impossible to say what may or may not work for you. however, it is always safe to assume that you should not lay down compression liberally, even if it is soft-knee because it might take away from the liveliness of the recording.
