This is a very interesting thread for me. I too have a Superline and after quite some time, am still experimenting with load settings.
ASPRIN, I assume you were running without any capacitance load plug until Radio Moscow came through. This would give you a capacitance of 100pF which is quite high and might itself sit on the music. I was surprised you felt the plugs were the reason for this. I too am waiting to find the right settings (for me) then order the Z plugs. I started off with plus of 100R and 1pF. I may yet end up back there with my Apheta cartridge.
I have found that after changing plugs, the results take a little time to be realised. It is not like flicking a switch so this adds to the time required to experiment. For me 500R is too much and the sound is very bright. Even adding more capacitance to tame this helps a tad but the overall sound suffers. I will try the settings with no plug in the capacitance slot over the weekend. I think the most I have used so far is 10pF.
I only just found out that the cap plus can be replaced with an R plug. Then you have the calculate the overall R using the 1/over formula. If you do this, does this mean the capacitance loading is simply the Superline default of 100pF?
BR - Dave