As sound quality is subjective, that really depends on YOUR perception.

For example: Many say that the Alpine CDA-117 sounds better than the 9887, Eclipse MK7200II sounds more "analog" than the P99RS, etc. But in the end, I sit in every vehicle with the favorite decks of car audio enthusiasts from old-school Denons and Nakamichis to the still-coveted Clarion HXD2 and all I can is that "I can't hear a thing". I think this is attributable that my ears aren't trained enough... but hell, 99% of the population isn't either. So I'd rather pay attention to your tuning settings such as crossovers or slopes as this will still be the cornerstone of your perceived sound quality difference. Unless you're the type of person who can hear a 0.5dB difference, I wouldn't fret over it head unit X sound quality to head unit Y sound quality.

Pare, my brother used to have a cheap Pioneer head unit that he coupled with an independent 24-band L/R Audiocontrol EQ and I find that it sounded very good. Heck, I'm using a stock head unit and most people would rate my sound quality to be "high". Factually, it sounds excellent for a daily driver.

It may be for a fact that a more exotic or expensive DAC or other audio component would yield a noticeable audible improvement. But after all these years, I think I'd be more happy with a spanking new TV on the wall rather than spending it on that "noticeable audible improvement"

Look for technical capability instead -- number of EQ bands, slope intervals, pre-outs, etc. ;)