Do you have any pictures of the Sirius unit you're describing? I thought there was only the XM tuner available for the 4Runner. If you don't have the SAT button on the HU (I've got a 2005 with NAV and single CD), will your unit work? I know the XM unit works by pushing the AM button until the SAT stations appear, even though there isn't a button labelled AM/SAT.
A place called "CoastalTech.com" I think had an XM unit and another place "metrotpn.com" had an XM unit for something like $240 a little while ago.