Not that my concurrence of anything Al says matters all that much since Al is a EE and undisputed A'gon techie. By contrast, I am not a techie, just a techie "wanna-be." But what Al says is consistent with my anecdotal experiences. I own an ARC tube amp with output trannies, and as Al said, the output tranny matches the speaker load impedance to optimally load the back impedance presented to the power tubes.
Of course, the moving target variable is that speaker impedance usually varies as a function of frequency response ... and some speaker impedances vary quite a bit. The practical result is that most folks just use the tap that subjectively sounds the best.
If you want to learn more about matching traditional tube amps with speakers, there's a number of threads that delve more deeply into the topic. I personally find it very interesting.
As to your specific question about biasing the tubes, I would be surprised that Jolida would instruct you to change tube bias to compensate for speaker load. At least that is my experience with my ARC amp. But ... as I said, I am not a techie. Call Jolida to be certain.