Radios, Intercoms & Inputs.

As my name implies I'm building a Zenith 601XL. The avionics I'm planning on
are as follows...

Garmin SL40
and a Garmin 496.

I know that the SL40 has a built in intercom and I assume it is good enough
for two headsets. My questions is is there an input for the external audio
that will be coming from the XM side of the 496? Or will I have to install a
stand-alone intercom for that?

Also, I have considered a secondary audio input for an iPod. If the SL40 is
capable of dealing with outside audio on its own does anyone have an idea as
to what I need to do to put an external switch in the system to switch
between the XM and the iPod?