How much plate voltage and current to use?
The trick of mitigating the triode's transconductance by using an unbypassed resistor in series with the Cathode Follower's cathode, cannot be used here, as the crossover network requires a very low impedance output, which adding the resistor would worsen. Consequently, the idle current has been purposely been chosen at a high 10 mA's. A 100 plate-to-cathode voltage and 10 mA's of current per triode will produce 1 watt of dissipation per triode. (If a different tube is used the B+ voltage will have to be increased to allow the alternative tube more breathing room in terms of bias voltage.)

Which sort of power supply should be used?
This circuit calls for a split rail power supply  with +/- 100 volt rails. Schematic. A single polarity power supply could have been used, but at the cost of an additional input capacitor and its biasing resistors and a poorer signal to noise ratio figure. A quick reread of November 1998, particularly the section on the trick used to lower power supply noise, will help explain why this is the case.

Because this circuit enjoys a good PSRR and the Cathode Followers work in strict Class A, the power supply does not need to be regulated. The split rail supply is easy to realize, as center-tapped transformers are readily available. One such transformer is made by Hammond and is available from Antique Electronics: P-T263AX. It comes with three secondary windings: 100-0-100 VAC @100 mA, 5 VAC @ 2 A, and 6.3 VAC @ 2 A. If the 200 CT secondary is hooked up to a silicon bridge rectifier, it will put out about +/- 140 VDC. This voltage can be dropped down to +/- 100 volts by including a 10 watt, 400 ohm resistor in each rail. This transformer is robust enough for a stereo 6 dB per octave crossover, but not enough for the 18 dB version, as its current demands are much greater: 70 mA per channel. With the 18 dB version, one transformer per channel could be used.

Once again, quality is better than quantity. Use lower value, but higher quality capacitors in the power supply; 10 µf of polypropylene sounds better than 100 µf of electrolytic.

Heater Concerns
AC or DC voltage can be used on the heaters. DC would lower the noise floor, would require more effort. A stereo 6 dB per octave crossover would use five 6DJ8's, which would require almost 2 amps of current to feed the heaters. A stereo 18 dB per octave crossover would use seven 6DJ8's, which would require just over 2.5 amps of current to feed the heaters. In both cases the Hammond transformer previously mentioned would prove unable to power a DC power supply for a DC heater arrangement. On the other hand, this transformer heater windings could be used  to feed tube rectifier heaters, one for each rail voltage; a 6BY5GA for the negative rail and a 5AR4 for the positive rail.