It dosent mater how many amps you have as much as it does the amount of power that will be drawn through the wire at any given time. I have been told that the best way to decide this is to find out what amperage your gauge cable is rated at(some have more insulation and less wire, and vise versa), then to check the fuse ratings on the amps..
Like for my case.. I have 1 4 gauge wire, 2 amps. One amp has a 40A fuse and the other has an 80A fuse, so 120 maximum would be how much my amps would draw at its peak before fuses get blown. So this means I run the wire from battery, within 18" i place a fuseholder with at least a 120W fuse, run the cable to desired mounting location then use a distibution block to split the power to both amps.
So really if your wire is rated to handle the combined fuse ratings of your amps then just use a distro block, otherwise upgrade the 4 gauge to a 2 ot a 1/0 gauge wire.
Hope this helps,
Lurius