Power wire gauge (specific setup)

I have seen a million guides suggesting the proper wire gauge for specific situations, but they all vary quite a bit.  I currently have about 14 feet of 8 gauge Streetwires cable running from my battery to a distribution block.  I then have 8 gauge from that to a Alpine 7894 head unit, and a Kenwood PS200T power amplifier.  The Alpine is rated at 27wx4 RMS and 60wx4 max.  There is a single 20 amp fuse on the power wire that came with the unit.  The Kenwood Amp is rated at 75wx2RMS, 150wx2Max.  The amp is bridged for a sub and the bridged power rating is 300W rms, and 600W max.  The unit has two 20 amp fuses, I'm guessing 1 for each channel. 

So here's my dillema.  If you add all that up, you obviously come up with very different numbers depending on what you go with.  If you go with amps, which to me makes the most sense, I can only draw 60 amps max from this setup.  Am I correct in that assumption?  If that's correct, the 8 gauge for a 14 foot run seems fine for my setup.  On the other hand, if I figure the maximum power output, it would come out at 840W and 8 gauge seems insufficient for that.  My guess is that the manufacturer's power outputs are over-inflated and that the total amp draw is a more reliable means of determining the wire to use, but I'm wondering what everyone else thinks.  It would only cost me about 20$ to run 4 gauge, but I'm not thrilled about widening the hole in my firewall, and running new cable unless the gain is significant.

My bad, I read your post as two amplifers, not as a head unit and one amplifier. 8 gauge will be fine for your amplifier.

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