Audio Mixdown Sounds Drastically Different From Stereo Out

Hello! I am completely new to Cubase and audio engineering/production as a whole, so please excuse me if this is an obvious question. When exporting an audio mixdown from Cubase (any file type), the mixdown’s audio quality is dramatically worse than the audio quality of stereo out. If I import the exported mixdown back into a blank Cubase project the audio is fine again, so obviously there is something going on with the hardware that I’m using. I have a pair of OneOdio headphones that are plugged into a Yamaha MODX 7 which is connected to my laptop via a usb which lets me hear audio from my laptop and keyboard simultaneously. I also own a 2nd gen Focusrite Scarlett Solo, and when I connect it to my laptop the same problem occurs: the mixdown’s audio quality is worse than stereo out (although with the Solo the mixdown isn’t as bad as the MODX). I’ve been using the MODX setup continuously for two or three years without any issues. The laptop I’m using is an Alienware m17 which is otherwise perfectly capable of producing high quality audio. In Cubase my audio driver is set to Yamaha Steinberg USB ASIO, so stereo out is reaching my headphones through my keyboard and not my laptop (changing the system volume of my laptop doesn’t affect the volume of stereo out, but changing the master volume or usb volume on my keyboard does). What could possibly be going on? My best guess is that my keyboard is doing something to the audio that my laptop isn’t (or vice versa), so when I listen back to the mixdown after exporting it’s all messed up. Although, any mixdowns sound perfect when played from my phone using headphones, so I’m not sure that’s right. I have tried listening to the mixdowns using my laptop’s default media player as well as Audacity and the result is the same, so my default player isn’t automatically EQing the audio or something like that. I know that I’m brand new to producing and my inexperience with audio mixing is probably somewhat contributing to this problem, but the fact that the audio that I’m hearing from stereo out and the audio that I’m hearing from the mixdown are so different lead me to believe that there’s something else going on here. What is causing this to happen? How can I fix it? Are other people going to hear low quality audio when listening to projects I’ve made in Cubase or is it specific to my laptop? Any advice is greatly appreciated!

tl;dr: Audio quality of mixdowns is significantly worse than stereo out when played back but fine when imported into a new project or on other devices and I don’t know what the truth is or why it’s happening.

maybe check your Windows audio chain - there may be sound modifications lurking in there.

EDIT:

a recent related thread:

You’re a lifesaver! For some reason mono audio had gotten switched on for output devices. All I had to do was turn it back off. Thanks so much!