No, you can fit a variety of comands - here's the relevant info from
Frank's Miata Page :
A210 820 4889 no Can-Bus
A210 820 5489 with Can-Bus
A210 820 5689 with Can-Bus and 'Speller'
A210 820 5189 with Can-Bus (US-Model)
A208 820 4089 is from a CLK W208 with CAN-Bus (like A210 820 5489)
A163 820 XXXX is from a M-class with no Can
The other bits are a canbus adapter. Steve very kindly supplied me with one, but you can obtain one from
MegaComm . Other bits are the gps antenna and various connectors. Possibly a cage to slot the comand into, but I'm not sure whether that is needed. Another forum member, Paul Grainger didn't use the cage. I'll have a complete list of what's needed when I install.
If your existing MB cd changer is the fibre optic one, then yes it will work. You're also very lucky

. Mine is a Blaupunkt and won't work

.
Cheers
Andrew