need help on wire gauges

So I'm hooking up a fosgate t400x4 which will be on 4 -2 ohm 6.5 mids and tweets,with a fosgate t1000 BDCP on 1 fosgate t1d415 (DVC) thats 1000 watts rms(fosgate always underated,even the amps birthsheet is at 1540 watts rms at 2 ohms).So,I know this is overkill,but I don't mind the money cause overkill doesn't hurt.Getting the big 3,and I'll have a 2500 watt cap,I'm gonna run 1/0 from the battery to a splitter,splitter will have4 awg pure copper to the t400(which will have at least 100x4 rms(about 29 amps)) then a 50 amp anl fuse to THAT amp.....then 2awg to the cap,then to the t1000 to a 125 anl fuse(or 100,not sure cause at 1500 it pulls 109 amps,prolly a 100 fuse say(which max is about 1500 watts rms,but prolly never even need it figuring the 15 maybe will run 1200 rms max on a deep note)so my question is.....about the grounds.....since the t400 is split on 4 awg and the t1000 is on 2 awg,should I just ground each amp with the gauge going into the amp straight to a chassis bolt?Like 4 awg ground for the t400 and a 2awg ground for the t1000? Or should I use a block?I was just gonna use the same cable gauges going into each amp coming out as a ground to the same spot.Or do i need to use 1/0 as ground for both amps being that's what i used before the split.I was thinksince it's overkill I could just use the same gauge coming out of the amps as a ground as goin in.Also far as the t1000 into the DVC 15 speakerwire is 4 gauge copper enough?or maybe go 6? Also 1 more question to add,since I have 1/0 positive from the battery do I have to have 1/0 on the big 3 coming from the alternator to the neg of the battery? Thanks in advance for your help...this is bustin my brain a bit and I'm kinda ocd so I like to be perfect lol.
 
Tricky, some of it depends on how long your power cable or speaker cable runs are.
Is this for use in an automobile? Sounds like it.
Do a google search you can find some of your answers there.
Also, go to your local welding supply, they have welding cable
and can even finish the ends for you. Draw a diagram and post it here.
It will help people figure out what you are doing, otherwise it is a long
pile of words that no one wants to wade through.
It only costs money.
I hope this helps.