Many are satisfied with the sound quality of unit Honda is giving; its over priced; but its exclusive (yet) as its not available in open market and is slightly better than Rockmars etc
This is tricky question...[a] if you have budget you can opt for branded systems with navigation; but be ready for spending handsome amount for them [b] you can install two head units; DrShaggy has done it in his 7th Gen Civic; but I might never do this and [c] you can try "Car Computer" thing
OR SIMPLY
Have a good audio sytem in car....and continue to use your cell phone for navigation? You dont need navigation every day...