After some thought (on the walk home from work) I decided to split the grating PCM synth sound across 2 Basslines, I then added a new PCM synth and did a live mix down. Still rough as anything but getting there I think :D
Apologies to anyone if I've plagiarized the melody that takes over in the 2nd half, it sounds awfully familiar o_O
It was there submerged in the last mix but to be honest you couldn't tell, you can really hear it now.
Let me know if I have though!