The reason is that most m-audio hardware are at -10 dbv for consumers gear compared to the +4 dbu of the professional gear. That's quite a margin in how much gain you can have at the input and how hot you can track as +4dbu gives a better signal to noise ratio.
Not only that, but there's also the fact that, professional sounds has always have compression, limiting and gain staging done that will boost the volume up, which is part of the loudness war that has been ongoing for the past 30-40 years. The more you compress, limit and gain the whole thing, the more you lose dynamic range. For rock.. that's not so bad.. classic and jazz. that's horrible.
You also have to remember that the meters in PT are not RMS, they are peak levels. There's vu meter
plugins that you can use that would help you see exactly what db you have.