vw factory ant use w/sat , nav

I need some help improving my current installation.  The car has three sat antenna's now, one inside for the Nav, one outside for the XM, and the original factory "shark fin" antenna that is not used.  Factory radio is out and replaced with in dash Nav w/add-on box for XM.  Would like to eliminate the aftermarket antennas and use the single factory antenna.

I realize there are limitations because the XM/Sirius antennas are powered, don't know if the Nav. antenna is powered.  Would need to find a solution that could provide proper freq. to XM and Nav without sending excess voltage they aren't able to handle.  The factory antenna services both via the same wire (can anyone confirm) but the lead goes only beneath the pass front seat (where the original Sirius unit was located) since the car was originally non-nav.

 Looks like VW uses Fakra SMB connectors.

Vehicle: 2008 VW R32 (aka GTI, Golf, Rabbit, many parts compatible with Jetta/Bora's as well), originally equipped w/factory 6-CD in dash with Sirius box (was underneath passenger seat)

Added Components: Pioneer AVID-D3, XM Sat unit (GEX-P10XMT) w/NavTraffic, Bluetooth (CD-BTB200), three COM boxes for error control/steering wheel buttons, 8" sub, 300w Amp.

Current In Use Ant. Setup:  Sat/Nav antenna on dash inside, XM/Sat on exterior rear roof just behind original factory

Goals: Eliminate aftermarket magnetic sat antenna's (2) and use factory original "shark fin" antenna while retaining acceptable Nav/Sat radio signal.

Purpose: Aesthetics, one antenna is better than three.