In the manual we suggest just lighting the LED which results in 30 mA per tube. If you want to use other bias levels you can measure them across the 15 ohm/10 watt resistor which carries the combined cathode current of the 4 tubes in that channel.
I always run tubes cool to get the 10.000 hour life. At full rated dissipation life will be in the 1000-3000 hour range. Multiply the current per tube by 460 volts. My number is about 13 watts. EL-34's are rated at 25 watt dissipation and 6550/KT88 are 35 watts.
I worked very hard to make the amp sound good at the lower (recommended) bias level so owners could get maximum tube life. In my experience, higher bias on my amplifier does not improve the sound though it certainly reduces the life of the tubes.