There is some decent information
here regarding upgrading from pre-NTG 2.5 to NTG 2.5.
However, as an owner of an '09 S211 with standard NTG 2.5 bluetooth, it won't stream music anyway. Bluetooth calls, yes, but it does not have the technology for music streaming. The car comes with a 3.5mm Aux input in the glovebox, which is inconvenient and poor when fed with the low volume output from an iPhone headphone socket.
The aftermarket CarPlay/Android Auto stuff from the chinese manufacturers like
Erisin seem to be the easiest solution, and one I am considering myself as I like the idea of it looking almost OEM. I am imagining poor sound quality and flaky operating system in this aftermarket chinese stuff though, would love to hear from anyone who is happy with their implementation.
Martin.