what is a better set up for sound quality?
Sound quality? Dayton Reference and IDQ are two great choices. IDMax is good but is not the SQ line. Don't assume that just because the SQ sub is cheaper, that the more expensive subs are automatically going to win. ID does not use a really good motor like XBL^2. The increased excursion of IDMax is going to come at the expensive of linearity and SQ.
You can also go for XBL^2 and underhung drivers like Exodus Audio, Creative Sound Solutions, Stereo Integrity, etc. If you don't mind the awful marketing of IA, you can go for Flatlyne - underhung, should sound good.
FLAT RESPONSE DOES NOT EQUAL SOUND QUALITY. It is very important - I'd even say the most important factor, but it is far from the only factor. In fact, without a linear motor and suspension, your frequency response is going to change with volume - potentially a lot. And I do not just mean the gain you have set, but also as the woofer cycles through the waveform coming in.
IDMax sounds fine, but it's not a SQ sub. It does not sound as good as any of the other drivers I mentioned. Will it be good enough? Maybe. For most people, definitely. I HAVE recommended it to some people in some situations, though I am not sure that I'll continue to do so with the future of ID going where it's going.