It's dependent on venue and equipment, but I would be pretty disappointed with the amount you'd have to spend to see Massive Attack to get crap audio. It can be done even at the stupidly loud volumes they pump out though; Nine Inch Nails at the O2 Arena in London was fairly well balanced for all it was very loud (I've heard louder, but not by a huge amount), as the instruments were mostly audible against each other and you could follow what they were playing quite well. Yet the first support band at that very same event had rather a distorted sound, and I could hardly tell if anything was coming out of the lead vocalist's mouth, let alone work out words most of the time. So even in a pretty good venue you have to start with good equipment and set-up to get good sound.
The only other experience I've had is mostly with local bands at small venues, and they're usually not balanced particularly well, or have equipment that just can't put out clear sound.
Nonetheless, an un-plugged orchestra in a half-decent venue just has a sound you can't beat compared to the volumes pumped out at the majority of amplified performances.
