Forgive my ignorance, but, isn't an Argyll jacket the "sports coat" of kilt wear. What you wear with the jacket would depend on the occasion. If out shopping for the day and the weather is cool, couldn't it be worn over a knit collared ****, even a tee-shirt. If you are going out to dinner a nice business shirt of a color that compliments the kilt.

As a sports coat it can be dressed up of a semi-formal occasion or down for casual occasion. IMHO