Hi Zig,
I feel your pain. I'm not very happy with my sony head unit in many ways, although the sound is good. Just not good documentation, misleading specs and bad android app. I am learning to cope :(
Anyway, I thought I would take a half hour and see what I could find out in the manuals for the three units, hoping you overlooked a hidden secret. Nope. Sony only mentions sirius in stating that it will work, in a marketing way. No doubt, you've read through these until your eyes bled. No mention at all in the connections pdf for the sony :( Doesn't say much about the bus either.
I hate to encourage you to spend more money on something that might not work, so please try to verify before you buy, and/or buy from some place that will take it back opened if it doesn't work. Perhaps one of these will make it work for you:
The cable that is plugged into the bus control in: https://docs.sony.com/release/CDXM60UI_install_EN_ES_FR.pdf
It says, "*3 Supplied with the marine remote commander" in the notes to the right.
On pg 9 of the scc1 manual: http://www.siriusretail.com/pdf/manuals/scc1_installation_guide.pdf
System 2, I believe would be the cable/converter mentioned above and included with the remote commander thingy. Thingy is a technical term, it is listed in the glossary of the PERL programmers book from O' Riley.
System 3, I believe is what you have now. Does the cable from snysnc1/unlink out fit the bus on the sony, or another connector?
Unless "bus" and "unilink" are the same, I think you need an adapter between the synsnc1 and the sony. http://www.siriusretail.com/pdf/manuals/SNYSC1_Installation_Guide.pdf says unlilink out "Connects to the ***UniLink*** connector on the Sony
headunit" I don't see unilink on any of the docs for your head unit.
The advertisement https://docs.sony.com/release/specs/CDXM60UI_mksp.pdf says "The CDX-M60UI integrates seamlessly with satellite radio Sony® Busadaptors so you can receive digital satellite radio broadcasts" So you need a Sony Busadaptor to make life seamless?
Just guessing, the feature will "wake up" when you connect it and the sony "sees" the input on the bus. Hopefully. Otherwise, perhaps that feature is defective, by failure, or by bad design.
If you do need an adapter to get it to the bus, and you want to shoot first and ask questions later, maybe you can find it on ebay. If it's cheap it's worth a shot without a return policy. Most sellers are willing to get better photo's and describe stuff to you, so maybe you can locate what you need there.
I hope this helps you, and certainly hope it doesn't hurt. I'm just paying back what the real pro's here have taught me and others.
Build a man a fire, he keeps warm for a day. Set a man on fire he stays warm for life!