What you are describing is referred to as passive horizontal biamping, JB. "Passive" because an active crossover is not being used to separate high and low frequencies "ahead" of the amps (the passive crossovers in the speakers doing that instead), and "horizontal" because each amp powers part of both the left and right speakers.
It is generally believed that when passive biamping is done with identical amps it is preferable to connect them in a vertical configuration, rather than in a horizontal configuration. Meaning that each amp is assigned to one speaker, with one channel of a given amp powering the highs of its assigned speaker, and the other channel powering the lows of that speaker. That way the two channels of each amp are processing the same signal, which eliminates the possibility that sonics may be adversely affected by inter-channel "crosstalk" within each amp. Also, it makes it possible to have shorter speaker cables, potentially minimizing the sonic effects of those cables.
That said, I’m not sure that biamping two of the 300B amps would make all that much of a difference in terms of allowing each amp to operate within its region of lowest distortion. While passive biamping reduces the amount of current and power each amp must supply, without an electronic crossover "ahead" of the amps they both would still have to output voltages corresponding to the full frequency range of the signal. And in any event the increase in the total amount of power that can be provided to the speakers would at most be only 3 db (i.e., twice as much). And the actual increase that is realized would be less than that much of the time, depending on the frequency content of the music and the crossover point of the speakers.
Finally, keep in mind that the preamp’s output circuit would see a load impedance corresponding to the input impedance of the amp divided by 2, since the two RCA outputs of the Freya are almost certainly driven by the same output circuit. It appears that your amp has an input impedance of 50K, so the Freya would see 25K when driving two amp channels. Looking at the specs for the Freya I would think that would be ok in the JFET or tube mode, but might not be optimal in its passive mode.
Regards,
-- Al