I have 2 Infinity's and I know that they are very good SQ subwoofers. I also know that sealed boxes are good for SQ, but is it okay to put those subwoofers in a ported box?
yes but make sure the box is tuned low to maintain as much sq as possibly. If you use a box that is tuned high you will lose alot of musical info below the tuning, and if you dont have a ssf you can easily bottom your speaker out since the box wont aid in the suspension anymore.
A proper ported enclosure can maintain excellent sq. Don't think with the mind set that ported= pure SPL and sealed=SQ because that's just now how it works. I would reccomend a ported enclosure for 90% of people looking for a nice sounding daily driver. You'll find taht if properly done it will meet the expectations of most people.