I don't think it's possible. Looking at the diagrams in the service manual it seems the navigation system is integrated into one unit with the bose system. All the controls and nav display are all connected to that one AV control unit, which is directly behind the audio controls in the dash.
You would have to just upgrade the speakers/amp which shouldn't be an issue and sound quality will be much better. Just get something like the Mtx Re-Q or JL Cleansweep to get a clean signal from the stock headunit and connect your new amps / speakers to that.
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SOLD 12/30/2011 2010 370Z Coupe Monterey Blue 6MT/Touring/Sport/Nav
F.I. CBE CF w/ 12" Res | V1 | SecondSkin | Stillen G3 | EVO-R CF B-Pillars | Volk GT-S Ti Gunmetal 19x9.5 +30 F, 19x10.5 +8 R | Swift Spec-R Springs
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