Well, this sheds more light on your expectations. If SQ is your number 1 concern, you might not want to do a Pioneer controller with Serato. There's actually a lot of complaints about this combination on the Serato Forums (vs. Pioneer or Rane mixers). Rather than repeat it, I'd suggest you check it yourself - Serato Forums | Serato.com - (https://serato.com/forum). There are even conspiracy theorists that think this is done deliberately by Pioneer to further support their own software, Rekordbox DJ (some of Pioneer's controllers are available in two versions of the same model - one for Serato, one for Rekordbox).What some people don’t realize is the dj controller is the starting point of your music! I am an audiofile who happens to have a sound company! I am a different kind of dj in my area, and my price point is above most in town,because I bring a lot of equipment and lights, and my sound quality is unmatched by any in my area! I bring twice as many low end cabs as I need,and way more power than I should,,,,, also I run 2 sets of Qsc 12.2’s for my tops! I do this so that I can run all of my equipment nice and easy and CLEAN! I want a controller to have a great d/a section with a lot of voltage output, good separation,low THD, great signal to noise,,,,and so on. We all know about GIGO!
The other issue, which I suspect you already know, is the hardware (in Serato) unlocks the license - you have to use the sound card in the controller - not an option to use anything else (like a high end audiophile one).
Frankly, my controllers are junk* compared to an SX3 or a SZ2, yet I think Serato sounds just fine - but I have Serato's Auto Gain set to 89db (the lowest setting) and make up for lost gain by feeding everything (controller and mics) into an outboard mixer.