Agree with Bartholemew.

Good rule of thumb is to avoid mastering or remixing anything you've recorded on the same day. After hours in a studio your ears become desensitized to certain frequencies, and when fatigue sets in, everything seems to mesh into everything else.

Come back the following day (or several days later), and give everything a fresh listen, and then start adding in whatever effects need to be there, and adjust and pan the individual track levels to your liking. Most professional grade studios have several different sized reference speakers ranging from large monitors, to small little computer sized speakers, so that you can gain perspective on how your tunes will sound in various formats. One rule of thumb for home studio enthusiasts is to NEVER MIX AND MASTER THROUGH HEADPHONES. False readings everytime, which you'll notice when you play those songs back through external speakers and find the track levels out of whack from what you thought they were.

Also when checking out professional grade studios to do demos, if they're working in analog formats (i.e. tape) you want maximum headroom or separation between the tracks, for more clarity. A 24 track tape studio should be using be using 2 inch wide tape. A 16 track, 1 inch.

When you work with 4 or 8 track home porta studios, that use standard (narrow width) audio cassettes, you discover how headroom is an important factor, as multi track recordings made on narrow tape widths tend to wash all the tracks into each other (a.k.a. "bleeding".) Sometimes you don't always hear the 2 and 4 on a snare drum or rim shot, and the reverb tends to wash everything out, even if it's only on the vocal.

Don't get me wrong, analog porta studios are great, educational tools for learning the basics of multitrack recordings, for song writing and home recording projects. For professional demo purposes however, best to use a more sophisticated format whether that means going into a full blown commerical recording studio, or find someone with a professional grade home recording setup.

With digital mediums, the higher the sampling rate, the more headroom. Anything over 24 bit, should give you the professional sound you want.