This could possibly work for you. Normally, it isn't best to use a different antenna that isn't rated exactly the same for the radio you are using, whether it is Sirius or XM. It is a concern of mine that over time it could damage the XM unit. But there is such a product that exists that will allow you to run two sirius radios off of one antenna. It runs off of RG6 and comes with two connectors to change from RG6 to SMB. Here is a link to the product:
http://www.tss-radio.com/sirius-home...it-p-4095.html