use 0 guage wiring and run the amp at 2 ohms. Since you have a upgraded alt you could probably run it at 1 ohm, but its not covered under the warranty at 1 ohm. i myself would probably run it at 1 ohm but thats because my friends have before with no problems. The amp puts out plenty of power at 2 ohms so either way you should be fine. From what i hear the hdc315's like higher tuning, so somewhere in the range of 36-40hz should be good.
edit: well seeing how you have the dual 1 ohm sub, 2 ohm to the amp is your only option. So wire the subs in series to get 2 ohms and you should be fine. Let us know how the hdc315 does off that amp, apparently some guys are saying minimum 2500 rms for that sub.