hissing sibilants

IMBW but I believe that the spec you are quoting is refering to the ECP1's gain if the internal or "self" impedence of the MC is 10 ohms. They do not actually state what the input impedence of the ECP1 is when using the MC setting. Delos recommends loading anywhere from 98 to 806 ohms so I can see how people are getting good results when loading the cartridge anywhere from 100 to 500 ohms. The ECP1 in MC mode must be directly coupled (no coupling cap between the cartridge and the first transistor) to the cartridge as the HI-FI choice excerpt on the Electro website states that some MC are effected by the DC voltage that it runs through the cartridge coils. Maybe Delos could answer how the DC would effect there cartridge... BTW when a dealer says 10 ohms would "kill" the cartridge he just meant that the voltage drops by half when the input impedence of your phone pre is the same as the internal or "self" impedence of your MC.

Actusreus,
IME (as well as the MC industry) finding the optimum load is by far the most important for achieving best sound performance of a MC. You yourself have found this out when you optomized your Delos with 200 ohms.. BTW there are strong advocates for 40 to 1 SUT not because they needed that amount of amplication but they get the best sound when the standard 47k input impedence of the phono pre is "reflected" down to about 29 ohms when presented to the cartridge. I myself have changed out the input resistor on my phono input to 3k to give my cartridge a 30 ohm load (as reflected through my SUT) which was the best overall sound from my Dyna.

As far as the .2ma of current that they are describing it's from the base of the transistors that are being used in the first stage of amplification. If you want to dive into it you can find threads on DIY forums as to which kinds of transistors, in what types of circuit topologies, that will present the lowest amount of current to the preceding stage, in this case the coils of the cartridge.