Pros use compression*, limiting, and “manual” gain-riding** for a “louder sound”. Modern [u]Loudness War[/u] recordings are very-highly compressed & limited, and sometimes even clipped (distorted). Dynamic compression and limiting (both with make-up gain) can be used to bring-up the overall/average loudness without boosting/clipping the peaks. (They do reduce the dynamics of your recording and if over-done they can sound like distortion or otherwise mess-up the sound.)
You can use those same effects/techniques, but of course professional mastering engineers have years of experience and a choice of expensive tools, so we can’t expect to get the same results “at home”. And, you might not want to “crush” the dynamics (if you’re recording/producing music) because some of us find that constantly-loud sound boring!
Can you suggest some optimal levels for gains (preamp, mixfade, and master) on the ZEDI10?
With digital recording your recording levels are not critical as long as you don’t “try” to go over 0dB. Pros often record at -12 to -18dB (that’s around 20% of the maximum level). You can use the Amplify or Normalize effects to bring the levels up after recording. Then, if it’s not loud enough you can try some compression & limiting to bring-up the “loudness”.
Don’t confuse dynamic compression with file compression like MP3. MP3 doesn’t affect the dynamics of the sound and dynamic compression doesn’t affect file size.
** With modern digital recording, the levels are adjusted in post-production/mixing with a process called “automation”. So it’s not really manual, but is done by-ear. In Audacity there is and Envelope Tool, that allows you to fade-up or fade-down selected parts of the recording.