Well in simple terms, 4 gauge isn't large enough for 3KW... ofc or not. Two runs of 4 gauge ofc would barely be sufficient and wouldn't have the current capacity of one run of 1/0 CCA. One run of 1/0 CCA is good for about 300 amps. One run of 1/0 OFC is good for about 350 amps. So, speaking in terms of Sky High prices, you can buy one roll of OFC 1/0 for $172.00 and get barely over the maximum current capacity that your setup needs or you can buy two rolls of 1/0 CCA for $160 and get almost double the current capacity your setup needs.
Not to mention, you can probably do all of your amplifier and big three wiring with 50' of wire... so CCA would be $80.00 while OFC would still be $172.00. And even if you only needed 30' of OFC, you'd have to buy it by the foot and it would cost you $109.20 and, you'd have to be exceptionally accurate with your estimating.
Your amplifiers take 1/0 power wire because the manufacturer specified that they be supplied with that much current capacity, not because they had extra 1/0 terminals laying around. ;-)