It is not in the market. You have to go to their website to download the .apk.
I just downloaded the siriusxm app yesterday and it was working fine. I then got the update and since then have not been able to connect as well.I called siriusxm and they told me to try uninstalling and reinstalling which I did but still no luck. I called HTC and they told me the same thing and they didn't have any issues or had heard of this problem and told me to try the same thing, which I told them I already had. The last thing they suggested was to try a factory reset but told me the phone would still have the same software upgrade when rebooted. Is there anyway to get the previous software without rooting? I just got this thing 48 hours ago and love it otherwise