So if you only have one SiriusXM receiver on your account, you can't stream on two devices at the same time. And they are pretty good at enforcing this.
I think this needs further clarification. I'm deeply embedded in the Amazon ecosystem, so what I say here may or may not apply to other streaming platforms.
I can play SiriusXM on any number of Echoes in my house with one subscription for my car. I can even play different channels on different Echoes IIRC.
I have a serious annoyance with the SiriusXM Alexa skill, though. It won't tell me what song it's playing! Alexa just answers, "This is <channel name>". So, if I bring up
Stream top music, sports, news and talk radio on SiriusXM on my home PC to find out what song it is, and even though the song comes up paused, at least one of my Echo groups, the pair of Dots (for stereo) with an Echo Sub, plays for about a minute and then says it can't play any more. Sometimes, if I check out the song played and dismiss the window fast enough, some of the Echoes elsewhere in the home can indeed remain playing. The only way I can listen to my Echos and figure out what song is playing (via PC player) is to have two accounts and two sets of credentials on SiriusXM.com. I did this for awhile when I subbed my wife's car as well as my own and that worked out well, except my wife never listed to her receiver at all. At least I got a free Echo Dot + Smart Switch for subbing my wife's car for a year. Obviously they weren't exactly "free" at the end of that sub.
I have 2 Echoes in a Savage, MD apartment, one at work which I play via my phone's hot spot, and the rest here at home in Fairfax, VA. I have no idea whether I can play my favorite channel both at home and the apartment or at work. This will make an interesting experiment. The streams would be going to two or three different IP addresses, so if SiriusXM sees that happening, then they may well kill the other streams.
I will leave one of my Echoes playing here when I go to work, and test this out this evening when I visit that apartment. My wife and I can get stuck in MD due to horrific traffic, particularly on Fridays. When that happens, we typically have a dinner date and then go the rest of the way home later.