As Andy says, the cab does not have a dedicated sub like the saloon/avant.
it does have larger front door speakers to compensate for this, 6.5" I believe (not 100% on that though).
Front Low (Doors)
Front Mid (Dash)
Front High (Doors behind wing mirror)
Rear Coaxials are only 4"/10cm I believe...
I think in all non-bose systems the HU has a two-channel amp for the front speakers, saloon/avant have a 3-channel for the rears and the sub, cab has a 2-channel for the rears. Bose systems have a separate amp, unsure if it's two amps or a single multi-channel one?