Audio Systems: RSE not working, rear speakers, dual source

Question
Dear Ernesto,

I have a 2007 Yokun Denali with the following codes
U42, Y91, UQA and UVA,but there is no UVB listed.
It came with a two slot radio for cd and dvd, my children used to watch movies and I listen to my music,I decided to replace the radio with a factory made one but with navigation, I bought a used unit #15925210, the new# is 20807046 denso.
however I took it to the dealer and install it, but they couldn't do anything about the rear DVD, my problem is:

1- Rear DVD screen is not displaying only the front.
2- Rear speakers output is very bad and low like if it was without Bose

3- Aux jacks at the rear controller are not working. so I cannot add another DVD player at the back.

Please if u know how to solve this u will be a great help. I read on the net that this unit comes with one audio component!! I didn't understand what does it mean?

Can I replace the UVA module with a UVB one? and where is it located?

Thx a lot

Answer
the 15925210 uvb was made for the 2008 vehicles
this radio will let you input 2 sources from the same 12 pin plug XM and rear dvd
sometimes the radio needs to be flash by the dealer to recognize the external sources

this radio don't have the dual source, some people have been able to flash the software from the
2007  and it work

2007 and 2008 radios are not the same, the software is not the same  and the 2007 will let you
use xm dvd and aux  
also this radios come in bose and non bose version

good luck