hissing sibilants

I have a Delos and if you're having sibilance issues, it's definitely not the cartridge. As others suggested, do you hear sibilance on all records, or only some? Just to give you an idea, I have a few pressings of "Synchronicity" by The Police and one of the copies is unlistenable because of sibilance, while the other sound great.

If you're having sibilance with vocals on all records, I'd check the VTA to make sure it is in fact neutral, which is actually tricky to get, and if it is, lower it just a bit to see whether you can hear a difference.

However, I suspect your phono preamp is not the best match for the cartridge for a few reasons. The manual for the Electrocompaniet phono preamp states "Gain 1 KHz Moving Coil (source impedance = 10 ohm)," which would be very low if it is in fact input impedance. I have my Delos loaded at 200 Ohms, but I've heard of others who have it loaded anywhere from 100 to 500 Ohms with good results, but 10 ohms is certainly too low when loaded directly into the MC input. When I first got my Delos, I called the Lyra distributor to inquire about the loading, and the person I spoke with said that loading it at 5-10 ohms would "kill it" (his actual words). (It would of course be different for a step-up transformer.)

Further, the gain for your unit is stated as 73 dB, which is WAY too much for the Delos. Your line preamp's gain and your speakers' sensitivity also come into play here, but from my experience, a gain over 60 dB kills this cartridge (my words). At an output voltage of 0.6 mV, the Delos does not need more than 55 - 58 dB of gain at the phono stage level to perform its best. When I switched gain on my phono preamp to 63 dB, the sound became strident, shrill, and overall unpleasant. It did not matter much when I lowered gain on my line preamp; the sound was just not right until I lowered gain on the phono preamp. In fact, it sounded like serious sibilance amplified to an uncomfortable level. At 73 dB, I cannot even imagine how aggressive and un-musical the sound must be. Something to think about.

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.

Jjrenman,
The gain value surely cannot be dictated by the internal impedance of the cartridge. From what I understand it is dictated by the cartridge's output voltage. You want to use the lowest value that provides sufficient gain for the signal. Tools such as the KAB calculator are useful to approximate what that value is. My own personal experience with both MM and MC cartridges and several different phono, line and power amplifiers confirms that it is critical to use correct gain to match the output voltage of the cartridge for the cartridge to perform its best. Too little gain and the signal will be too low to provide enough volume, while too much gain (at the phono level) will result in a sound that is shrill and strident, and it becomes all but impossible to adjust the volume to get the sound right.

My concern about using this particular phono preamp with a Delos seems to be confirmed by this review that's reprinted on the preamp's page:

"The only test result that might be significant is the very high (in context) current it passes through a cartridge's windings, up to 0,2mA. It certainly won't do any damage, but with some cartridges might affect the sound. That apart, this is an extremely fine piece of kit and is strongly Recommended."

I thought the current went from the cartridge to the phono stage where it gets amplified, rather than the other way around, which the above-quoted text would suggest. It's possible that it was incorrectly translated into English, and it simply means that the preamp uses a very high voltage to amplify the signal, which might not be ideal for medium or high output MC cartridges such as the Delos.