Why in the settings window while playing on virtual keyboard, the instrument sounds beautiful, but in the arrangement it sounds dull and with tension? I mean saxophone, trombone and so on. The long notes became ugly as if the instrument carries a bag of 100 kg.
. . . . Does the quality of the sound card affect software synthesizers during Export or Mixdown? . . . .
It can, however I also have the Realtek HD Audio and it does not affect the quality of the sound in mixdown or rendering.
Check the following:
there are no enhancements turned on in the Sound, Playback devices as shown below
Open the mixer (M key) in Music maker and check there are no effects applied at track or master level - the image below indicates that an effect is applied at track level (left arrow) and at the Master level (right arrow)