The tubes are always the same in these amps, at least in terms of type. The circuit is identical to the final HEV90 version on the amp side but you have the benefits of not using the cheapest possible parts as Sennheiser did on the HEV90 (single turn carbon pots, basic 600mW resistors and lovely Wima MKS4 coupling caps) and far better layout and PSU. The only real deviation from this is my take on the HEV90 which uses different dissimilar tubes (which are both triodes) with different feedback setup but the rest is the same.
It's so Sennheiser that they never mentioned this evolution of the amp anywhere. Not subtle changes too as the first two versions are very poor with limited power and high distortion.