If it helps, I recorded a few drop-C# clips with the HD a while back:
here &
here (actually, the
remix on Pg2 is better...)
Never tried it lower tuned.
As for coil-splitting, I don't the neck sounds particularly good split, but IMO you don't
need to split it as it already has one of the best
clean tones on the planet :) I have no use for a split bridge so I've never tried it...