I think the K5 Pro is a flawed product and shouldn't be bought.

You kinda say it yourself in the review: in neutral setting the audio sounds flat and lifeless. Reason for that is, when the treble/bass knob is neutral position it doesnt have a flat frequency response, the bass is still 3-4dB too little and the treble also falls of like 1-2dB.

So its not a DAC with optional EQ, its a DAC thats always EQ'd. You either have too little or too much bass. Is impossible to make your headphone sound like its supposed to sound, which for me personally isnt acceptable for that price, I would rather listen to an apple dongle than to this DAC.

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.

I cant agree with that, I think the HD560s is in nearly everything better than the HD660s. The Hd560s has bigger soundstage, better imaging and better bass extension and sounds overall way more correct/neutral to my ears. The build quality and comfort are better on the HD660s tho.

I love the HD660s for movies, podcasts, videos, everything thats vocal focused. It has a kinda warm/neutral tuning that is just easy to listen to.

But for music and especially gaming i prefer the hd560s. The hd560s has so much better soundstage, imaging and depth perception than the hd660s, its not even close. The HD660s can image very well but its small stage and relaxed treble make it quite bad for gaming, especially if a lot of things are happening at the same time.