I have a Pioneer HU, and I bought the auxillary input (RB20) with rca inputs. XM IP connector to the aux input box, MP3 player into the rca jack, then the IP from RB20 to the IP in the HU.

Turned on AUX and I hear both XM and MP3 (Dell DJ). Basically i guess you need to somehow turn off the XM in order to hear the MP3 player.

Anyone have a solution besides FM Modulator?

That's strange!
Which pioneer HU do you have? Is your XM box a pioneer also? Only thing i can figure is maybe it's an older HU?

I think IP BUS should detect signal from the RCA inputs and turn off or ignore the XM box if I understand the RB20 correctly (don't have one yet myself).
Might be worth a call to Pioneer if you get no answer here - sounds like the RB20 might be defective (long shot).

Sorry - don't have a solution but I am interested in the outcome as i currenlty have a DEH-P960MP HU, and may be trying the same thing in a few months. (currently have Omnifi going though RB10 RCA line in. Maybe planning on changing to RB20 and adding IP Bus sat radio)

Its the DEH-P7600 model (04 version). After reading manual again, this is what I found:

"In order to listen to external devices attached
to this connector, turn the external device‘s
power on, put it in play or other operational
mode, and set the main unit’s source selector
switch to “AUX.“.
If the main unit’s source is a multi-CD, the
sound signals from both the multi-CD and
the external device will be heard simultaneously,
mixed together. When listening to
a multi-CD, make sure the power supply to
the external device is switched off.
As the main unit does not control the power
of external devices, they must be turned on
and off independently of the main unit.
Do not connect any devices to this connector
which have an RCA output of over IV
and do not have any volume control. They
may damage this unit. Device which do have
a volume control should have the volume
adjusted to a point where the sound does
not distort."

So basically there is no on/off switch to the Direct XM (the two small boxes, one pioneer adapter the other the universal tuner). So to me this is not really an auxillary input option, unless you have cd changer with on/off switch. So unless someone has any ideas I guess i have to wait till something new comes out or a HU with 2 individual inputs.

Hope this helps someone thinking of adding MP3 player to Pioneer HU with the direct XM.