Vellfire 2011 Import Which Company Installs best head units?

I have recently bought a Vellfire import and am really pleased with it.  A 2.4X hybrid version.  Drives well and all the functions work like electric doors etc.  I had an adroid head unit fitted when I bought it, but the stereo sounds muffled.  I see that the head unit only displays 4 speakers and I wonder if it is underpowered for the car?  The sound system should be great?!   And the video screen at the back mirrors the input.  At the moment I can't play any video as it seems Prime Video / Netflix / NowTV all have code which stops you from mirroring their output to a screen via lightning cable.  Would the original head unit have been better?! I also saw that there was an auto-volume-leveller function in the original unit which would be useful as my kids always ask me to turn sound up and down when watching a film in the car.  

Can anyone recommend a good app for streaming video other than Z link which I have?  And can anyone recommend any Vellfire import specialists who would be able to recommend installing a better sound system that drives the speakers better?  And a bigger screen fitted at the back? 

Your thoughts are appreciated!