One of those issues is that I can't plug my phone in via USB which I use for my music through my Kenwood head unit and get traffic and weather through the Garmin since the IPhone will only support 1 accessory at a time and for some reason the bluetooth connection to the Garmin makes the phone think it is an accessory. They think its because of Pandora on the phone as well as on the Garmin.
I don't have a 590 but I use an iPhone and a SENA headset and other Bluetooth items. I'm struggling to understand what/how you are trying to hook these up.
Are you using a headset or the speakers for output?
Are you using Bluetooth to connect the Garmin and the phone to anything OTHER than each other? (Not counting the iPad, I mean the combination that you WANT to work.)
Bluetooth headset?
I suspect you may be able to get around some of this if it's another BT device involved.
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