I'm not familiar with the phonostage you have but if you put two loads in parallel, such as 220 ohms an 100 ohms, you will not get the two numbers to add up - you will get a smaller figure. In this case it would be 69 ohms.
I recommend you don't get too hung-up on the load impedance and what is "correct". It isn't all that important. As a general audio electronics principle the load impedance should be a lot higher than the source impedance. "A lot higher" means about ten times, or more. For example, microphones have a source impedance of about 200 ohms and microphone preamps have a load impedance of about 2000 ohms. Things like CD players usually have a very low source impedance of a few tens of ohms, but maybe a few hundred or even up to about 1000 ohms. They're fed into preamps with a load impedance (or input impedance) of about 10k, which will be more than 10 times the source, whatever it is. Loudspeakers present a load of about 8 ohms and should be driven from a source with an impedance of less than 1 ohm. Transistor power amps can easily have a source impedance much less than 1 ohm. Valve power amps have a source impedance not quite as low, but should still be much lower than 8 ohms.
Anyway, the load impedance on an mc cartridge may affect the tonal balance slightly, but not very much. I suspect that when many people claim to hear tonal differences they're either very slight or they're actually hearing a slight difference in level which they mistake for a difference in tonal balance.
BTW, "Mprince said he runs at 500ohms with his 103... ", but how many options does he have?