Nothing wrong with going with a bg sealed box. if the sub can perform well in it. For best SQ in my beetle I'm runing my 33KX in 3.4cu.ft sealed and it's just what absolutely sounded the best in my setup. 1.4 cu.ft is the largest Focal reccomends for that sub.

Looking at your first post the problem I see there mainly is that you wired the coils in stereo. Using a 4ch amp is okay, but it's always much better to bridge the connection so that both coils are getting the EXACT same signal. This should help out whatever sub ou choose to go with next.

 

look into the infinity perfects....might be exactly what u need.....?????
discontinued...... but just perfect subs......e-bay...???

 

http://toronto.kijiji.ca/c-buy-and-sell-electronics-12-Phoenix-Gold-Xenon-DVC2-Subwoofer-500Wrms-1000W-peak-RARE-W0QQAdIdZ103658706

yo!! found one man!!!

 

10" xenon here: http://cgi.ebay.com/ebaymotors/Phoenix-Gold-Xenon-X10D2-10-800W-Dual-2-Ohm-Subwoofer_W0QQcmdZViewItemQQ_trkparmsZ72Q3a1234Q7c 66Q3a2Q7c65Q3a12Q7c39Q3a1Q7c240Q3a1318Q7c301Q3a1Q7 c293Q3a1Q7c294Q3a50QQ_trksidZp3286Q2ec0Q2em14QQhas hZitem290303128228QQitemZ290303128228QQptZCarQ5fSp eakers

 

I have one still.it sounds best in a small sealed box..72cu. and it needs 500w of good power.the alternator needs to be at least 100 amps.optima yellow top.good 4 ga.with a cap.power supply is critical especially when the sub wants to play low.and 12's are good for around 40 hertz.....

 

is your 100.4 still alive?what set-up did you go with?