As I see you almost randomly changed many parameters and now want to fix lacks. Instead of this I recommend you take a factory preset that is most close to your desire and change it a little to a certain direction. Most factory presets are pretty good. Modartt already have done all work and just provide you a list of factory presets that cover almost all tastes and applications. For 90% cases you should not touch anything. For 10% cases you just need to change 1-2 parameters to achieve a desired sound.

If you want learn how a certain parameter affects the sound, just change only that parameter and listen the result. Official manual have great explanation of all parameters and how use it. Also see this page. The most hard thing is the mics positions; it's affects sound in a weakly predictable way, so I recommend in most cases don't touch it at all.

For anyone who is willing to help, how can this custom preset (based on the D4) be improved?

MIDI files downloaded from the Classical Piano MIDI Page, http://piano-midi.de/midi_files.htm)
Rachmaninov, Prelude No. 5
http://www.forum-pianoteq.com/uploads.p...ev01_A.mp3
Mozkowski, Etincelles
http://www.forum-pianoteq.com/uploads.p...ev01_B.mp3