Right first of all, you cannot remove that single CD player at all. It is the MMI headunit, CD player & radio all in one.
So you can add a 6 CD changer alongside it effectively giving you 7 disks to play from. When you add a 6 CD it will go into component protection and skip every 2 seconds, a dealership or an independant with online access can clear this only, no one else can.
Also as you have MMI Basic and the AMI is not supported, so the best option for USB/Ipod is the Dension GW500, using this with a 6 CD would give you the best combinations.
If you want any of these options fitting then give me a shout I have them all in stock.