To match the 660nm content of qb96 elite you would need to add like 5% 660nm deep red. For 750 watts that would be like 37.5 watts. Rapidled sells solderless red diodes that make it very easy to build supplemental strips. You could make 3 rows of 5 660nm cree xpg3 diodes and have more deep red than the qb 96 elite. Those diodes run at 4umoles/joule so they would bring the efficiency of the qb 132 to a similar efficiency that the 650R.
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www.rapidled.com
I agree its a compelling alternative although your numbers aree slightly of: at 750mA or 1.65w these xpgs will run approx 3.5/j at 25C and unless you match the diode count of almost 2300 white diodes its going to be hard to get to diablo efficiency. But you know what, with a build like this it matters very little the spread out nature of the build gives you an extra advantage in spread and photons not lost to walls compared to more compact builds. Many ways to skin this cat.
Ive been recing the qb96 lately due to easy build and all in one together with the huge capacity they have for any future projects, having enough to double the wattage by justt buying s drivers is a nice thing.
Incidentally our build is very similar: spread out but its in an open space in an aisle which makes access easy. 3200 lm561c over 1x1.5m aapprox at 480w.