In theory there shouldnt be that great of a difference, the thing that sucks most with onboard audio is the high output impedance, which could cause some bass bloat with low impedance headphones.

However, I would be carefull with that Fosi DAC tho, it might actually change the sound. I had the fosi k5 pro, which is related to the Q4. The K5 pro noticeably changed the frequency response, reason for that are the bass/treble knob. even when the bass and treble knob are in neutral position, the frequency response isnt flat, it still had less bass and treble than it should have.

That may make a bass/treble heavy headphone like the cloud2 more neutral, which could be interpreted as better sound, but can make properly tuned headphones like the dt900 pro x sound worse.

Honestly, i would just avoid all dacs with treble/bass knobs and would probably not get anything that hasnt been properly tested by a 3rd party.