For my BT Audio solution on my 2014 Nismo with the Bose HU, I bought the:
HomeSpot NFC-Enabled Bluetooth Audio Receiver for Sound System
and the
UGREEN 3.5mm Auxiliary Audio Flat Cable 90 Degree Right Angle Compatible for iPhone, iPad or Smartphones, Tablets, Media Players Black 6ft/ 2m
From Amazon. I spent less than $40.00 total. Stashed the unit under the center console, plugged the flat 3.5mm 90 deg audio cable in to the aux input.
I get the full benefit of the existing Bose Head Unit sound and satellite along with the BT Streaming audio of my choice off my Android phone, Nexus 7 or iPad air. I am very happy with the results. I don't get the HU deck controls, but the phone/tablet/iPad all have reasonable controls that come with the app of Choice. I use pandora, Amazon streaming audio and sometimes Sirius Internet radio. On Long trips Netflix or a movie play well thru the speakers. The wife enjoys the diversion while I do the driving.
Obviously i could have replaced the whole head unit. Might have been better audio quality, but in my experience the audio quality is no better or worse with the $40.00 solution of the $600-$800 solution. Feel free to challenge my assertions, but if you don't try it first you'll never know.
Just my 2 pennies worth.