Hi mate,
That orion sub would be an absoloute animal in a good box! Im telling you, it would probably have the power to smash your windscreen in, or blow out your sunfroof!
I would power it from the hifonics amp, due to it being £100 cheaper and 400rms more than the orion, even though the orion is more efficient and better built, i couldnt justify spending the extra £100 on it.
There is currently a guy on
www.talkaudio.com selling an RE xxx 15! Its brand new, and he wants £250. This would quite literally piss on the hcca, and it will also be more listenable too! Another guy on there is selling an RE MX 15, which is also a high end SPL sub, and he wants £150! Either of them will run fine of 2-2.5 kw rms, and both will give you an unruly amount of bass!
With regards to alternator, it would be worth uprating it, as the standard is only about 60-70amps iirc, but it might not be totally necessary, as long as you have a good main battery (yellow/red top), 0 gauge cabling, and a second battery in the boot.
If it was my choice i would go for the RE xxx 15! These really are the ultimate when it comes to SPL!
You are willing to give up your whole boot though arent you?? Cus you're gonna need atleast 4cuft i'd say!