Here is one other item I have run across when a radio has a very low output to the speakers. The radio is programmed for if it does or does not have an amplifier.
If somehow, during your sat antenna install, you got across something incorrectly, the radio may need to again be programmed for the correct output for with or without amplifier.
The normal radio without amp, the speaker wired go directly to the speakers from the radio.
With an amplifier, the output is programmed to a low level output from the radio to the amplifier. Then the amplifier will boost the output to the correct level.
Most likely what I would do here, since you didn't have a problem until you attempted the satellite antenna install, I would go to the back of the radio and switch the front and rear speaker wires, and check to see if the rear speakers then work, while the fronts then go low.
If you have no amplifier, then you know the problem is within the radio. If when you switch the front and rear speaker wires, you find that the rear speakers are still at a very low volume, then you know that your problem is either in the amplifier, or the rear speakers.