Questions about central bass and external devices

Just picked up my new All4 S Countryman (will post pics when it stops raining, probably about March).

Generally loving the switch from derv to petrol, but the stereo in the new one doesn't seem as powerful as the one in my old All4 Cooper D. The old car had the Boost Radio (not HK) and the new one has Visual Boost, which I thought was the same but with a screen to display track info and menus.

I generally listen to music through an iPod Nano that is connected to the USB and Aux ports via a Y cable. On the old car, there was an option to change the volume of the auxiliary input from 1 to 6. On the new one, this appears to only affect Aux input and not External Devices, which the iPod is now classified as on the Visual Boost screen. Is there somewhere on the menu system to increase the volume of external devices? I have set the iPod volume to maximum and changed the EQ setting to make it more bass-heavy, but am not sure it makes any difference when connected with the Y cable.

I also thought there would be two speakers, one under each of the front seats. If there are, they are not making themselves felt.