The difference between 4 and 6 ohms internal resistance would not by itself account for any difference in tonal balance you may perceive, comparing a 100R load on a XV-1S to a 1000R load on a TKR. If you're happy with 1000R, I'd say leave it alone. If you want to try 100R, the good news is that the latest iteration of the nude Vishay (aka Texas Instruments) resistors are a little more sturdy than were the older types, and 100R is not so low in value as to reduce the useable output of the TKR. They've added a kind of brace that links the two legs, so it is not quite so easy to pull the entire assembly apart, by accident. Knock yourself out.