If there's one thing I love about mixing live audio is the control you have. There are a million things that can conspire against you but at least you're the one driving and you don't have to worry about how the band will sound on someone's iPod.
That's the classic problem. You make a mix in the studio and you love it. Then you have to send it off into the world and hope that it translates well on every crappy car stereo with one speaker out, every clock radio, every pair of headphones, and every bedroom stereo with the bass and treble boosted all the way up. The last is the worst part to me. I've been places a number of times where I tried to show people with smiley face curves on their stereo EQs what listening flat sounds like and the immediate response is, "That sucks! Put it back!".
People like their big bass and crispy highs. It sounds good. The problem is, after a few minutes it starts to wear on the ears and in short order the lows and highs are maxed out. I'm guilty of it myself though. I like to feel the bass when I drive and I boost the highs (a little) to fight road noise. To a certain extent I guess it doesn't matter. The fact that most audio out there on the internet is 128k MP3s (or worse) means that people are really just after the groove and the hook and don't care so much about how it sounds.
A brief pause for everyone with 4.7 terabytes of lossless music on your hard drives to swallow hard and get back to reading.
That's the simple fact though. Most people are listening to crap files on crap equipment and we somehow have to make our stuff sound good on all of it. That brings us to some pretty weighty decisions when it comes time to make those final mixes. Do you keep a scooped EQ handy to patch in and check your mix? Do you keep a pair of tiny speakers on hand to hear what your mix will sound like on a computer in an office? Do you hear it on your MP3 player? In the car?
The big boys do all that and more to make sure things will translate well. But most often those are just checks at the end. The best of the best don't check at all. They know their gear and know how their mixes will translate. For the rest of us it's a matter of working toward that confidence level. But know that it's good practice to do your mixes flat and then see how they sound on hyped systems.
Don't fall in to the trap Brethren of the Knob and Fader. Make a pure product and then let the public screw it up if they want to.