350z oem nav voice how to retain it?

Hello all! I am a long time visitor and first time poster here. Great wealth of knowledge here! My question is somewhat complex and not one that I have come across too many times. I could not get any input on the Z forums, so here I am! I have an '06 350Z with OEM nav. I plan to replace the OEM Bose sound system with a complete aftermarket system. I want to retain OEM navigation guidance voice. A small number of members on our Z forums have achieved that by using a transistor and relay combination connected to the HU's cell mute wire and connecting the nav output wires (7.5-9v signal) to a dedicated (non-amplified) speaker behind the dash. You can read the details in the first post here if you'd like: http://www.my350z.com/forum/showthread.php?s=&threadid=18919 But the thing is, I would like to transmit the voice signal to the aftermarket amp that will be powering my speakers so that it would play through front, rear, or all speakers and sound loud and vibrant like it currently does. Is that possible? I will be upgrading my stereo system in the near future (yes, the HU will have a cell mute wire) and am the kind of person who doesn't turn a screw without having a complete plan laid out. I will be doing the install myself and am perfectly capable of that. What do you pros think? Have any of you had experience with this? Would greatly appreciate your input. Thank you.

BUMP. No one has any input! You guys are pros at this stuff. I am really desparate for some info on this. Thank you.