Well, an 8 ga. should handle the draw from both amps, so using a distro block from 1-8 ga. to 2-8 ga.'s should be fine. If you want to rewire it now with a 4-ga. split into 2-8 ga.'s and have more headroom later on in case you upgrade, that'd be good too. Either is fine, and it's really a matter of preference. You're going to be running 8 ga. directly to each amp either way, and since 4 ga.'s not really necessary at this point in time, it doesn't matter if you do it now or later.

Just don't forget to fuse the main wire near the battery and if your amps don't have built-in fuses, near the amps too.