Well it looks like you decided on the S4 version and to wire the four subs in series/parallel to a 4ohm bridged EP4000. That'll net you about 600w per driver. Risky with no SSF. Just be careful. All it takes is one big explosion on a movie you're unfamiliar with and CLANK pff pff... I'm all too familiar with this sound having reconed three 18" drivers in my HT over the last few years from overexcursion at < 15 hz.
Personally I would have opted for the S2 version and ran them two drivers in series to each channel of the amp. Easier load on the amplifier, better damping factor being unbridged, and more than enough power to take the drivers to overexcursion. This configuration would net about 325w per driver, and the Fi's reach Xmax in IB at just over 300w.
It sounds like your order's almost ready at Fi, so if you end up with the S4 version I would recommend wiring them in parallel pairs to a 4ohm stereo load on your amp. The EP4000 puts out about 820w/ch in 2ohm stereo, so you'd have 410w per driver which is plenty of power, and running the amp unbridged is preferable really unless you need every last drop of power.
BTW if you haven't gotten your EP4000 yet just cancel your amazon order and give Zzounds a call. They're an authorized dealer and will price match Amazon -5% with free shipping! I just bought two of them from Zzounds last month, and it came to less than $260 ea with no tax. I saved about $80 altogether vs Amazon because Amazon would've charged me sales tax in California.
Anyway good luck. Let's see some pictures!