I do not know much surrounding the touch screen and I had toyed with different ideas about how to get my Reatta updated with Bluetooth. I haven't been a fan of the FM transmitters, but the one at the link below has worked extremely well with my 88 reatta. Mine defaults to channel 87.7, which worked perfectly, and I programmed preset button 1 on my GCC with this channel. The sound is really quite clear, and this unit has the option for an AUX cord, and an SD card along with Bluetooth and it was only around $17. It's really nice because you can control the volume on this transmitter, along with play/pause/forward/reverse tracks. I was quite impressed for $17!
https://www.amazon.com/gp/product/B018E0I01I/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
On a side note, this is an awesome unit for giving you the option to have TPMS on your vehicle. I have one in my other vehicle and havent installed one in my Reatta yet, but they work quite well and mount easily on the dash without any messy adhesive and it's solar powered so no wiring at all is required. Another excellent buy for $40.
https://www.amazon.com/gp/product/B07QYS2J5R/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1