I have been playing w/ my Avalanche here lately too.Running a single in DD1508 s4 on an ia20.1 in a kinda 6th order. Right now is pretty much just the shell for my 2 dd3515 box w/ the dd1508 in 0.8cuft tuned to 40hz. Its sick for ~600w on an 8", but has VERY steep roll-off below 35hz. The 8" just totally unloads.
Thinking about reconing one of my 3 DD3515's to a 10" and playing around w/ that in a chambered 6th order //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif (quazi-8th order) That is unless someone wants to buy a d1.5 DD3515 w/ carbon cap (hint hint)
If those T/s i worked with are truly accurate, you should have a hell of a peak and still keep VERY low roll off. (though i have found that the t/s some manu's post are complete bs)
good luck w/ the build!