I have it installed yesterday 8 84 EH el on my Poweramp egl 820/35 instead of the original lamps. Recommended by our friend and guru Gillou, they also recommended to me by the sound lab technician.
They are certainly pricey, but worth it. I could compare them with Sovtek el 84. These are certainly two times less expensive, but the difference is huge. The EH sound rounder, warmer, less aggressive to the ear. They are also much more balanced across the sound spectrum (the Sovtek were more glaring, had less bass).
In short, an expensive investment but oh so effective.
I put 9 because of the price (but hey, not all Poweramp 8 lamps like mine).