Maintaining silver color

Hi guys. I'm a licensed cosmetologist, I teach instead of being behind the chair so my experience has been a little limited to only using the color line at my work, so I'm not super familiar with other lines unfortunately.

I colored my friends (male) hair silver using the silver metallic color from Kenra (Guy Tang's line). I lightened him twice to a white blonde and then we colored twice with the silver because the first round was way too light- as to be expected. He's only shampooed twice since doing it and it's faded significantly. I have him set up with purple shampoo to use and I'm going to pick up a toner/color for him to do at home.

I'm just curious what kind of experiences you guys have had using the color (the color is beautiful! just fading quickly) or if there's another line you'd recommend. Since I'm licensed I have access to all lines that are sold at licensed stores, so that isn't an issue. I'm not sure if I should go Pravana or keep using the Kenra (maybe go permanent instead?)

Thank you!

Edit: Mods I can submit licensure verification tomorrow (Monday) when I have access to my license.