I can only speak about the old hydra. My impressions of both units. Both restrict sonics on amps, better off with a good power cord into a decent outlet / dedicated line, The P600 is much more restrictive than the (older) hydra. I can see plugging the amp into the hydra, but I found it marginally better to go into the wall. The hydra excels on digital, allowing more ambiance and flow. It creates a more lively presentation, in my opinion. The p600 does work well on digital and makes the presentation much clearer, bass solid, and very uniform and balanced. Both are quiet. The p600 does make minor video benefits on TVs, uses up more energy, adds heat to the room. The hydra can benefit from a better cord than the stock cord and is hyper sensitive to vibration. Maybe the hydra 8 will improve on that. Overall both units have merit, the P600 for solid controlled, uniform sound, verses a more lively organic, spatial presentation.
