I've had two goes at changing the head unit in my 2007 9-5.
Firstly I put a top level Kenwood satnav system in place of the original in 2013. That Kenwood model was very unreliable and map updates were expensive. So two years ago I fitted a Pioneer DAB unit. It is just a radio head unit with AppleCarPlay (or Android alternative). All the satnav, music etc.is from my smartphone. When I fitted the Kenwood I hard wired it because there were no fitting kits available. However, I have since fitted a similar Pioneer headunit in our 2010 9-3 Carlsson and I used a fitting kit from
www.incartec.co.uk. It was a plug and play installation, apart from dropping the back edge of the headlining to fit a DAB aerial in place of the shark fin. Everything works including all the steering wheel controls.
All the Saab 9-5 headunits are wired and basically to an industry standard. The odd quirk which a good fitting kit will deal with. My Saab has the separate amp and that was no problem.