hissing sibilants

How do you know its not something else like a metal tweeter? If the problem really is with your TT setup, how old is the Delos? Phono cartridges sound awful until they are fully broken in.

Btw, it is sort of obvious, but did you also check that your cartridge is properly aligned otherwise? You only mentioned the VTA, but even more important is the overhang, azimuth, proper offset angle, etc. I'd start there to exclude an improper set-up as the cause.

I think you need to adjust the VTA by ear. It is very difficult to get the optimal VTA alignment by just looking with the naked eye. Select a record with plenty of silibant sounds and adjust until it sounds right. If you have the same recording on CD that will give you a benchmark, so you are not trying to adjust something that was recorded too hot.

agree about the phono stage....it is the most forgotten art of vinyl, that you have to find the best match for your cartridge (either loading it properly or the best match step up transformer....)

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.