I switched between the two 'modes' (full linear ??? and triode ???).
Full linear was 'livelier' and more 'in your face' (sound stage way forward compared to 'triode').
I was HOPING to hear the famous 'tube softness' compared to the solid state Mac 2125, but listening memory (time for switching from one amp to the next) was not strong enough to make that obervation unfortunately. A lot more 'listening training' is needed!
The owner did switch to EL34 for a week or so (borrowed tubes); I need to check back with him how HE felt they compare with the stock KT-88.
I have not seen a 'power rating' for the amp, but was very impressed with the bass even at higher SPL, and certainly no signs of 'compression'.
Wish it had a PRE OUT (it has the strangely named PRE IN to run as power amp).