I have not personally heard the Automobile Mass and quite honestly have never heard of it, but I will so some research and let you know.
As far as going with a ported box, are you looking for sound quality or volume? The reason I ask is that the sound quality of sealed is far superior to ported. Every enclosure has ups and downs.
Sealed is very accurate and small but needs a lot of power
Ported is at least 3db louder, needs less power but is larger and not as accurate
Bandpass is very loud but inaccurate and very large
If I remember correctly you have hella power, if you are going for sound quality (I am assuming you are ie...ID horns), I would suggest sealed.
About the horns, these got very popular in the ninties in the competition circut. My experience is that they sound very good to a RTA (real time ananlizer) but leave something to be desired to the human ear. Conventional speakers sound better to ME. That being said, ck out what I replied to Jose's post about front speakers. As far as ID mids and subs go, I think they are some of the best I have heard.
If you are looking for more output from your subs, ck out the new Kicker Solobarics, decent sound quality sealed, and unbelievable output ported (needs lots of power though).
[This message has been edited by 89lx5.0 (edited 05-30-2001).]