enclosure modeling for kappa perfect10.1

Why not use the recommended vented box?  Per http://manuals.harman.com/INF/CAR/Boxes%20and%20Parameters/P10.1d_f.pdf

It's a lot easier to make a sealed box oversized than it is a ported box.  Note the in-car response shown in the graph;  a peak at 35-36 Hz, which should be very good for this, or just about any, sub.  If I were in your shoes, I would use what's recommended.

Look at it this way:  it wouldn't be far-fetched to think that if this sub performed better in a larger vented box, Infinity would have recommended a larger size.  It would be easy to go bigger than 1 cu ft...(whereas some subs really need much more volume but the manufacturers keep the limited space of the vehicle in mind when they recommend a smaller size).  But in those cases you're still talking about at least 2+ cu ft per sub.  So, for Infinity to keep this at 1 cu ft is telling to me, in itself.

And to answer your last question, no, a vented box will not give you greater SQ than a sealed, but this subwoofer will perform best in a vented box (according to the EBP found in the parameters).  And you will maximize SPL this way, too.

My recommendations, other than already said are:  for more SPL add more cone area and amplification.  For better SQ switch the OEM deck for an aftermarket model.  You're system will always be limited in SQ using a speaker-level signal.  I use the OEM deck in my car, but I realize the limitations it imposes on my system.  (...still sounds good but I would hesitate to enter an SQ contest ;)

As long as you have the parameters of that sub correctly entered in your WinISD, and you understand how this program works completely...experiment with box volume.  Enter the volume of the manufacturer-recommended box incl. port size and look at the results.  Use the input tab to put in total RMS power that will be applied.  Then, if you want to experiment in making changes, work little by little from that point.  Check the port noise using the SPL chart, rear port air velocity.  Set your chart to read ft/sec at rms power.  Keep it under 100 ft/sec by adjusting port diam and length, if needed.