Proper 0 Ga Wiring

[BIGMANNYC]

hello all i have a nissan armada with a current system based on old and new items as follows : i currently have 5 amps ,1 rockford 250 old school powering 6 tweeters 1 lanzar on each door and two earthquakes on top dash near windshield , 1 rockford 800w 4ch powering 4 x 6" soundwave mids one on ea door , 1 crunch 1400w 4 ch powering 4 x 8" celestion midbass spkrs in a box , 2 jbl bpx 1100w crown series powering 4 x 10" 15 yro kicker solobaric single voice coil subs in a 8 yro custom spacesaver bandpass enclosure , with a rear eq crossover and 5 yellowtops 4 for audio ,1 underhood ,one 250 amp nations alternator , 1 audiopoipe front control and a jvc doubledin head unit , 0 ga 200a fuseholder from front batt to stinger isolator then to 2 ,4 ga wires together (shop didnt have 0 ga?) going to rear 5 farat cap then dist block to smaller amps then a 4 ga going into a 0 ga sub amp fuse holder and out from fuse holder via 2, 4 ga wires , one to each jbl 1100w amp that each amp is powering 2 subs in enclosure (1100w per 2 subs) = 2200w on 4 subs.......i will be upgrading to one visonik 4000w rms amp to power 2 x re audio 12" xxx series subs 4000w peak ea in a custom ported spacesaver enclosure from finecustomworks (46"w x 15"h x 16"d) to keep trunk room without sacrificing bass....... my questions are : is it reccomended to keep those two 4 ga wires together from front batt forming a 0ga for power? i would like to swap them for a true 0ga.......and for the 4000w amp will i just use a seperate 0 ga , wire from the first yellowtop batt into a seperate 5 farat cap for sub amp then to current 0ga sub amp fuseholder?...in 0 ga and out 0ga to 4000w 0 ga amp in for power.?..........my nephew sugested using a second seprate 0 ga line from front batt to rear for 4000w amp with a seperate fuse but i think one is good? because i thought the amp gets its power from the extra batterys.........any suggestioins would be greatly appreciated. ps beleive me it sounds mean but i still have not achieved the groung shaking , storewindow flexing , hairraising bass i want !!!!--- u guys know what i mean but hopefully after this upgrade it will do it? 6000w.