phono stage question

At 0.5 mv output I would think that is normal if the VTL and your amp both have moderate-high gain.

I looked at the Helikon's specs and see that the recommended load is from 100 ohms to 47k-ohms. The MM section of the VTL is probably loaded at 47k-ohms. So if the cartridge sounds "bright" to you in the highs, that is the probable cause... But that shouldn't hurt anything as long as you like the sound.

This also probably means that if you ever try to use a high output cartridge you'll be back to barely being able to move the volume control, even on the lower gain MM inputs.

I am not familiar with the phono stage of your preamp but some havve adjustable gain. did you look at the owners manual?