Thanks Jochen, I'll do that.

ccfj1 - That looks like a good option, I've drawn it out on paper so let me see if I have it correct :

Parts -

1) 61.13.8.377.072 - Male Plug x2 - same as CD I-bus plug.
2) 61.13.0.006.663 - Female termination x6 - 3 in each of item 1.
3) 61.13.6.931.929 - Female plug x1 - to accept CD I-bus plug from CD loom.
4) 61.13.0.006.664 - Male termination x3 - fit into item 3.

Procedure -

A) The existing I-bus loom (male plug & female terminations) will be disconnected from the CD player and connected to the item created by parts 3 & 4 above.
B) A loom of 3 wires will then go from 3 & 4 to one of the plugs (male plug & female terminations) created by parts 1 & 2.
C) A 'flylead' will be created by having a second loom of 3 wires going into the same male plug (1 & 2) as in B above. This plug (with 6 wires coming from it) will then plug into the CD player.
D) The flylead created in C above will be terminated in the remaining plug (1 & 2) which will then be used to plug into the I-bus interface.

Please let me know how the parts arrive, i.e. with wires attached to the terminations or not, and how the set up looks. I've found a large white connector in the area around the CD player and Nav unit from which the I-bus looms to those 2 units originate, so I can always tap into that as an alternative.