I wouldn't think you'd need aluminum. Some of this stuff is marketing hype. As long as the cabinet is sturdy (IE doesn't resonate at all) you could make it I think. I do think your underestimating the difficulty of building the crossover. I doubt all the like drivers are wired in simple parallel. One option you might want to consider is bi or tri-amping the speakers and then using something like the Behringer electronic xover. This removes any speaker interactions with the
crossover. Speakers are definitely not a 8 or 4 ohm resistive load. There are other advantages to driving the speaker directly by the amp, including.
No inductors. You just can't get as "ideal" of an inductor as you can a R or C.
The power levels in the electronic xover are lower, so higher precision parts can be used in the low level xover. Damping factor will be better. Even fantastic inductors in series with the woofers will have some resistance, degrading the amplifiers ability to control the cone.

More tweakable. The Behringer or other xover can twiddle with the crossover freq/amplitudes with a knob.

Downside of course of all of this is you need 6 channels of amps for stereo... What I think would be a really fantastic setup would be if Outlaw would dump out digital for all the channels with a protocol packet for volume. Then if they added a product that could eat the digital bit stream and cross it over to 3 channels with FIR filtering. Output that to a 3 channel amp and voila, a general purpose amplified crossover from direct digital inputs. Then either with an external box or internal processor, time align and frequency fix the three channels with a measurement microphone.
Probably better to do that external to avoid duplicating for each channel I know it sounds expensive... Think of the advantages. Each speaker has a power plug and a digital input (which could maybe even be wireless...)