I'll take integrated nav over cell phone or Garmin/Magellan any day. Not only do you get a bigger screen, but you also don't have to worry about your battery dying on you. Cell phone nav apps use a buttload of battery life. If you're on a road trip and don't have a car charger, you'll have a dead phone in about an hour or so. Same with the Garmins, et. al. I was reading up on a Garmin and it said the battery expectancy was about 2 hours. No thank you. I'm not one for having wires and such running all over my interior or those suction cups stuck to my windshield or those flimsy brackets mounted in some awkward location.
Nope. Gimme good ol' factory integration! Not to mention it's WAY more than just a nav system!
You can't get the Shaker 1000 option with the electronics package because the NAV system doesn't have RCA preouts to send a signal to an amp. You could still get the NAV system along with an aftermarket amp/sub but you would have to split the signal from the 8" subs in the shaker 500. (I specifically asked the parts guy at the dealership about this) This would make the 8" subs not as loud and the fit of an aftermarket sub probably wouldn't be as good as the shaker 1000 but overall it would probably sound much better than the Shaker 1000 and you would still have the NAV in the headunit and full SYNC controls.
I have seen some aftermarket sub boxes that fit nice for the 10/11 Mustangs, but they are a little pricey. Ive upgraded my door subs to the Shleby/Kicker ones and I feel they can use more power. What I was going to do is get a nice 4 Channel Amp, perhaps a RF T6004 or an Alpine PDX F6 to run the door subs and a trunk sub. it would be 150 Watt for door subs and 300watts for trunk subwoofer, and it should be more than enough to fix any bass that is missing.