Amplifier displays "CUR"
The "CUR" display means that the amp is drawing excessive current and the protection circuit is activating. Too low impedance or shorted speakers will cause the amp to draw excessive current.
The Alpine V12 is a Class D mono amp with only one set of speaker outputs. All versions, M301, M501, and M1001 are only stable to 2ohms. Assuming that all 6 of your connected subwoofers and speakers are 4ohm and they're all connected in parallel, the amp sees a .67 ohm load, far below it's rated impedance.
When brand new, the amp could probably operate at low to moderate volume levels without drawing excessive current. But as electronic components age, their tolerances change and they become less able to withstand excessive current or mismatched impedances.
I'd get a 4-channel amp and drive the 4" speakers off the front channels and the 6X9's off the rear channels. And just power the subs off the V12 making sure that they are connected to show a minimum load of 2ohms.
Hope this helps.