Hi,

So you have a Sirius Onyx EZR.
You need a vehicle kit that has a line-out dedicated cable or You can buy them separately.
You need I think a 3.5 mm plug-in port. Can be on the front or back of the head unit.
It may be labeled for MP3 or something similar.
I didn’t notice it in the YouTube video that you sited, so that might be an ouch.

If that radio can send out an antenna signal, there’s a cable that has a relay built on it that cuts off the incoming antenna signal. The cable inserts the Sirius transmitted signal.
It cuts in whenever you turn ON the Sirius radio itself. Your radio stays a radio out to the speakers as normal.

On my other units there is a menu to dial up and change output frequency to pick dead spot of NO station on the FM band in your area. I use 102.7 for an example.
If you don’t have the cable then you have to keep moving the Sirius weak transmitted signal to another dead spot.
Have you tried putting the body of the radio or it’s tiny antenna almost on top of your car’s antenna?
It can only reach a foot or two.
The FCC clamped their buns on their first “Sportster” units. They could feed half of a small house with a signal.

I have a share of knowledge about SiriusXM since I have a lifetime paid for subscription that we bought when I owned some stock in Sirius early on. The subscription was about the only dividend I got. It was $300 almost 40 years ago. I got my return when I see what they want now, ouch
Both companies chopped at each other’s necks until XM sold out to Sirius.
Sirius needed money for their backup satellite, at the time per FCC regulations and only the biggest money was going to survive.
As we know it wasn’t all that it was cracked up to be. I live where there are lots of trees or buildings blocked it.
Satellite radio is still flopping, IMO, with using the Internet and cell towers being a clue.
With that, its becomes three ways to pay. So much for some free communications on our “public” airwaves.

Hope this helps saving your investment in both.
Contact Sirius support and tell them what you have.
They will gladly stiff you,(:) but you can shop elsewhere.

If you have more questions just ask the board.

Phil