Once we have isolated the computational and neurological correlates of access-consciousness, there is nothing left to explain. It's just irrational to insist that sentience remains unexplained after all the manifestations of sentience have been accounted for, just because the computations don't have anything sentient in them. It's like insisting that wetness remains unexplained even after all the manifestations of wetness have been accounted for, because moving molecules aren't wet.