Hi leggy, if your MB pro runs Catalina then it is most likely not a 2011 model. The latest Mac OS that the 2011 MBPs can run is High Sierra. So, better check out your model by clicking on the menu bar Apple logo and choosing “About this Mac…. ” and then search the appropriate firmware installer for you machine. I haven’t used a bootable USB installer Stick for my updates. I have installed the OS on a USB drive and booted from that. Regarding the firmware version, you (and other’s who are coming here by search engines) should be aware that every Mac generation has their own firmware versions (and version numbers), probably because the hardware is a little different. So, regarding the early Macbook Pro 2011, 17” model and probably also the 15” model, I am quite sure by now, that Thunderbolt firmware 22,1 and the Port-Micro Firmware 2.1.3 are the most recent versions. And in addition to that, I happily found out that the updated Thunderbolt can now run a Thunderbolt 2 dock, which it couldn’t before.
I have had the chance to see it myself, including some testing. The Mac Mini was the 2,3 GHz i5. To cut it short: The system was slow, flickering monitor, the cursor (and the entire system) was freezing occasionally, and only HDMI was working. The Mini was booted from an external USB drive. The system was installed on a MBP 2011/Thunderbolt, from the original installer. The same problems occured as SL was installed on a MBP 2007 - from a retail DVD to the USB drive, and updated to 10.6.8. System profiler has recognized all hardware in both cases. I have also checked some Hackintosh sites for tips. But it seems that it is easier getting a Hackintosh to work with Snow Leopard, than a 2011 Mac Mini!
I would like to bring this article to your attention (this was written a few days and answers later): http://www.zdnet.com/blog/government/how-to-install-snow-leopard-on-a-brand-new-lion-based-mac/10652 Summary, as I have understood it: The author has installed Snow Leopard on the 2011 Lion Mac Mini. He has done this while booting from another Mac and connecting the Mini in firewire target mode. Then he has used a regular (retail?) SL DVD that he has bought before to install the system on the Lion Mac. He mentioned that he wasn't sure if Thunderbolt is working. In the talkback someone suggested installing Snow Leopard via virtualization. Interesting. One thing I don't understand is, why has he updated the Mac OS to 10.6.5 and not to 10.6.8? Something else I couldn't find in the article was, which Mini model has he used?