Are ICs important? Yes.
Do quality ICs (and all of ICs, speaker and power cables in general) make a difference? yes ... and the effects are much more graphic as one moves up the equipment food chain.
But the pre-amp to amp IC is just one link in the array. The entire IC - speaker - power cable array matters ...big-time.
I cannot agree that your notion of the ICs between the pre-amp and amp can be allowed to fall behind as the laggard in the chain .... just as with quality-build source versus a cheap alternative ..... garbage in = garbage out.
Again, the effects are also exponential as one moves up the gear quality (and price) food chain....full stop.