Does anyone have experience matching an Icon PS1 MKII with a Soundsmith Zephyr MIMC Star?

Music Direct are misinforming you.

Loading the Soundsmith cartridge below the recommended 470ohms load will result in awful sound.

You need to find another phono.

Soundsmith specially states a 10:1 ratio SUT is perfect for their low-output MI such as the Star - Transformer use with Soundsmith MI/Fixed coil designs | Soundsmith (sound-smith.com).  A 10:1 SUT should yield 470-ohms load to the cartridge.

However, the Icon manual icon Audio clearly states 100-ohms which does not make sense since their literature on the separate SUT -icon Audio states:   The impedance of a transformer varies according to its load, so in this sense they are self adjusting.

Contact Icon Contact Us | Icon Audio and a get a specific answer.  Does the 10:1 SUT actually load the cartridge at 470-ohms.  Tell them you are using a Soundsmith low output MI that needs 470-ohms.  

I have to suspect Icon installs a resistor across the secondary of the SUT, thereby reducing the load seen by the cartridge to 100 ohms, instead of the expected 470 ohms. Either that or the base load resistor at the MC inputs is 10K ohms instead of the standard 47K ohms. Either way, the problem is easily remedied. But I agree that the seller gave bad advice to ignore the issue entirely.

I have a low output Soundsmith cartridge (Sussurro MkII ES) and it sounds perfect through a 1:10 SUT that shows it a 470KΩ load.

I think you mean 470 ohms, not 470,000 ohms.  But you would not want to load your Sussuro at only 100 ohms.