Poor reception on jbl Mbb319 Sirius Ready AM/FM radio

First question is if you ever spilled a soft drink into the radio such that the AM/FM/SAT switch gets sticky?
2nd, do you have any way to pull-out the radio and borrow a magnetic-mount Sirius antenna to temporarily test and see if the antenna on the vehicle is bad?
If passing the first two tests, then it's likely the whole radio unit has to be replaced with a model from a similar year. Actually, the audio quality you get from an XM Onyx will be much better than the Sirius radio in the Chrysler vehicles, and you can just use the AUX input on the radio for playback.

Once you change the radio to Sirius, change the channel to channel 0 (zero). It should show the Radio ID on the screen.

I would highly recomend a magnum dynalab ST2 antenna. You can't go wrong with that.

The "hard wired" version that you speak of apparently only refers to the power supply.Do you have a seperate display for the Sirius unit? Now, you failed to mention the type of radio (factory or aftermarket); so, if you have to use an "empty radio station" then you have an FM modulator. This modulator could wired or wireless. The wired version interrupts the vehicle antenna wire and the station on said modulator is usually preset to either 88.1, 88.3,88.7, or 89.1. There is no need to power this modulator up, it comes on when then Sirius comes on. One way to check for power is to turn on the Sirius unit and tune your radio to an occupied Fm station. Wait a few seconds and listen to the reception. Turn off the Sirius unit, the reception should improve for the occupied station. If it is a wireless FM modulator it also has preset stations that you can change but, extending the wieless antenna will greatly improve your reception of the Sirius stations.

The electrical cord acts as an antennae for this radio. Uncoiling the cord will give the best reception for FM. Rotating the radio (and built in ferrite bar antennae) will give the best reception for AM listening.

You will find the maual you need by using the following link :

http://www.prospecelectronics.com/JBL%20MR6%20manual.pdf

What you'll actually need in order to get Sirius is a satellite specific receiver (the JBL SIR 2.5 Satellite Receiver). That should come with the antenna you need.

Check antenna connections at radio and antenna assy.. Poor connections will only receive AM and hardly any FM

I have noticed various changes in my invehicle FM reception as well. There should be a external antenna that came with your car kit. This is precisely for these types of issues. It is designed to run along the windshield inside the car closest to the Cars radio antenna. It should plugin to the bottom of the cradle. Then tune it into a clean FM station (one that has no local station on it) and position the cradle and/or ext. antenna till you get the best reception in your vehicle. It could very well be that the antenna has come has loose on your car stereo backplane. You would probably notice decreased reception on regular AM/FM stations as well though.
Your wifi reception/functionality is a completely different animal and has no bearing on the FM transmitter in the car cradle. When your on wifi your not receiving signal from a sat. anymore just simply streaming internet audio like your computer.
Good luck.

Did You pay Sirius for their service?