No issue with a three way line array speaker. I like a version that has a two way line tower with dual stereo sub woofers for the bottom end. Essentially, that is what my latest line array design really is as I'm using sealed 4.5" mid-bass woofers that work down to a 70 Hz F3 point. Thus the lower octave and a half is covered by the subs. Too often a designer will try to extend the mid basses by the use of a ported cabinet but that can lead to bloated bass vs. the faster transient response of a sealed box.

Regarding the Parts Express RS90 that isn't out yet: I'm not holding my breath on that driver. If you consider it as the next step down in the RS line then you have the RS125 driver as its slightly bigger brother. The RS125 has relatively low sensitivity and aluminum cone break-up modes that must be taken into account. I suspect that the RS90 would suffer those same shortcomings as the RS125 unit but likely an even lower sensivitity to go with similar cone break-up issues. The RS90 would likely be OK for a line array application--you would cross to a tweeter line lower than you would if you were using the RS90 as a midrange driver in a conventional two-way speaker. That wouldalleviate the cone breakup issue. A line array usuage would also mitigate the sensitivity issues with the RS90.

No easy answers.

Jim