2006 RRS Audio/screen probles

[mograt]

Hi, and appologies as I am sure this has been covered before. I spilled a small amount of coffee in front of the control screen, which now longer works. The radio screen is still lit up but no audio. Having trolled through some posts, I believe that the Harmon Kardon radio unit is used to drive the control screen, and it is often suggested to replace this and put the radio in the boot with an extended optical lead whilst replacing the radio with another unit and amplifier combination. But if the radio unit has a board or something blown and has stopped the screen working, surely it will still not function? Does this mean that the HK radio has a pre-amp installed ? is there a direct replacement for this that can solve the audio and head unit problem? I am looking for something that works, but the main issue for me is getting bluetooth back so that I van use my phone. If necessary I can use a sat nav if needed to replace the control unit. i see that there are after market replacement units that offer touch screen control, but I dont want to go down that route and expense if the HK unit is trollied and renders putting in a new unit pointless.
I have also seen suggestions of doing a hard reset of the vehicle. Is this even worth trying in this case?
Sorry for all the questions and thanks in anticipation of any help.