The dongle has a SINAD of 99 and it’s other measurements add up to be as transparent and clean as any modern DAC, it’s in the upper half of DACs on earth. They’re all designed to be transparent and flat, they are universally flat and clean have been for like 30 years, the problem of “the perfect DAC” in terms of its intended purpose has been solved for $8 or less than $100 if you want something more luxurious or with other features. a lot of what a person thinks they hear (and yes, we are all susceptible to this, I am, the most “golden ear” on earth is as well) is very, very minor differences that don’t equate to “better” amplified by some confirmation bias or / or placebo. It’s okay to have this, it means a person is human and you don’t have to worry about being a KGB cyborg sleeper cell.

There won’t be noise from an Apple dongle because that’s not really possible, at least not in terms of the digital to analog conversion, there could be some other reasons for noise. The dongle is like 60-70 SINAD clicks above the closest DAC thats even borderline approaching levels where it wouldn’t be transparent and clean conversion. You can’t make something that’s audibly transparent more transparent, it’s just transparent or it isn’t transparent and there’s no signal or source the dongle won’t make transparent. You can reliably use it as the control and benchmark for clear conversion of other devices from that. You may have some small differences DAC to DAC but these are going to be quirks or flaws in the DAC, they do have sort of “a sound” in a lot of use cases but it’s more dependent on the chain in totality than it is just the DAC.

I’d consider looking at your EQ stuff before I’d attribute noise or distortion or deficiencies to the DAC, if you haven’t already I’d evaluate them without EQ on and then see if the EQ causes or worsens any differences you don’t like. It’s incredibly rare for a motherboard to have a “better” DAC but if it wasn’t an afterthought in design they’ve been putting more of an emphasis on them.