https://www.tindie.com/products/justtech/bluetooth-module-volvo-v50-s40-c30-c70-xc90/

pretty easy to install, took awhile to ship but I did receive it and my life is 100% better lol. No need for expensive grom just open your radio and install this with a couple flex cables.

 

What do you mean by upgrading the audio? The stereo? The speakers? Both? It was my understanding that the P1 cars were difficult to makes stereo changes to.