Unfortunately, you provide no real information that could lead you to a answer. As a few of the things one would need to know:

What Effects are in play on these sounds? - they are both heavily effected;
"Analog" mp3 -- certainly a Chorus, and a LPF that is almost completely closed, hardly any high harmonics
"Simple Air" mp3 -- sounds like a Phase Shifter, and again a very closed LPF, hardly any high harmonics

The lack of the high harmonics and the movement provided by the time delay effects causes some strange tricks on your ears - I do not necessarily hear distortion in the sense of crackling or the like.

When you recorded this to Cubase - did Cubase report any CLIPs (indicated by a red marker)? When you play audio with Cubase the meter provides you with a CLIP indicator, if, at anytime during playback you overload the channel a red bar will appear and remain (so even if you are not looking, you can know if you exceeded the recommended level). That would be more of indicator of trouble than anything else.

Within the Effect processing you have the ability greatly change the sound. The movement within the pad sounds comes from the Chorus or Phaser... the 'closed in' character is definitely due to the Element's Filter settings - you have no clarity in the upper frequency range... and that is not a criticism, just a statement of the nature of the Analog pad sound -- it is meant to be dark, and in the background - when you have a time delay, be it a Flanger, Phaser, or Chorus that motion it causes can sweep through the harmonics in play, that gives it the movement/undulating... the sweeping is happening across the frequency range but the FILTER is shutting the upper harmonics almost completely down, so there is a 'clutter' of what would be high frequency content that is smushed together...

Can you give us some details on the process you used to create the Cubase Mixdown... that is was this recorded in stereo? Was it meant to be stereo? Are stereo effects in play? Did you maintain this stereo during your audio recording and mix down process? Can you load the Cubase data and check for CLIPs?... Cubase meters will also show you the maximum volume reached by the meter. (Ignore clips at your own peril, even if you cannot hear them directly, a red indicator leads to harsh sound... your sound is not harsh as much as it is 'filtered'... I don't think distortion is caused by overload, I think it is the nature of the Filter combined with the time delay's sweeping movement.

Let us know.

Thank you very much for help!

The recording and mixing process in Cubase was very simple. I recorded MOXF Factory presets through USB into Cubase stero track, no additional processing.... No clipping occured. RMS is around -18 Dbfs, I even didn't touch the volume faders...

I hear the sweeping movement.... It's strange I haven't notice the distortion before..

I’m not sure it qualifies as “distortion” in the record level definition of distortion. It is ‘distorted’ like a visual image would be seen through water... the darkness in those sounds is what we describe as ‘damp’ darkness (underwater). Try opening the filter on the sound... it will ‘dry’ it out, add clarity, definition, focus, and the perceived ‘movement’ will have more light to be seen (heard). Record it again with the same levels, etc.

On Analog pad sounds typically filter cutoff would be assigned to MW (if a time delay effect is adding movement, the MW is usually the choice for filter cutoff) when MW is the filter this allows the user to set the Wheel to the timbre they want to work with... the MW holds its position so it can be used for quick customization.

At different filter cutoff freq settings listen closely to how your hearing perception changes as more of the frequencies are audible...
If you think of the most basic low pass “filter” is placing your hand in front of your mouth while talking. The person listening continues to hear you but the hand in front of your mouth diminishes the high frequency content (which travels in a straight line). The low frequencies travel around objects as they spread out. Low frequencies will work their way around objects—this is why when next door to the room with the loud sound system all you hear is the low frequencies. The lows hit the wall and spread out, they move around it, they move it.. the high frequencies hit the wall and reflect back into the room. You still hear the music but with less intelligibility.

As your hand covers you mouth completely, sound can still be heard, but exactly what you say becomes ‘distorted... did you say “walk” or “talk”, “see” or “free”? The less well the high frequencies are heard, the less intelligible your speech becomes... you fail to distinguish subtleties of the speech that let you understand what is being said.

The intelligibility is ‘distorted’ by the lack or restriction of the high frequency content. Hope that helps in thinking about sound and frequency content.

Thank you!