If you don't want to mess with adding amps and a sub then look at a set of Kicker DS 6x9's and CS 6.75" Door block off plates from Sounds Good Stereo along with sound mat in the doors. These particular Kicker series speakers are designed to run on very low RMS wattage like that from factory head units, sound amazing doing it but can handle plenty of additional power if you decide to add a 4 channel later on.
Adjust the F/R fader 2-3 clicks to the rear to produce a better sound stage in the cab and tweak the EQ in your audio streaming app of choice.
This is all I did to mineand it sounds nearly identical to a B&O. Just lacks that tiny little bit of low end from the sub frequencies Otherwise it's the cheapest and easiest improvement you can do for the non B&O factory sound system. Best part of all of this is no Forscan coding or custom wiring and can all be done in a couple hours.