The 100-ohm load will not sound "bad" with these cartridges, either the SL or the EL, but the SQ will be colored to a degree by the effect of the load resistance on the HF response and on total gain. It’s OK to like it that way. Lots of guys load down the Denon DL103, which has a similarly high internal resistance, even below 100 ohms, and claim to love it.
But it should be a simple matter for any competent tech to open up the chassis of a phono stage and replace the phono load resistor with a more appropriate value. I would suggest 1K ohm and forgeddaboudit. If the LOMC gain is being generated via an SUT, then one trick would be to increase the value of the load resistor that is across the secondaries of the SUT, to a value that results in the desired higher impedance being seen at the primaries. For that, the tech would need to obtain information about the turns ratio of the SUT, as well, from the maker of the phono stage.
But it should be a simple matter for any competent tech to open up the chassis of a phono stage and replace the phono load resistor with a more appropriate value. I would suggest 1K ohm and forgeddaboudit. If the LOMC gain is being generated via an SUT, then one trick would be to increase the value of the load resistor that is across the secondaries of the SUT, to a value that results in the desired higher impedance being seen at the primaries. For that, the tech would need to obtain information about the turns ratio of the SUT, as well, from the maker of the phono stage.