Building. sound board, ceiling defractor.

In my garage I have a nice little system, Ayre AX5 integrated, ARC DAC, Paradigm Anniversary Inspiration speakers, dedicated power etc, etc. 
Since the little system is in the garage where I park cars, do carpentry work, drink beer and such, it was necessary to put the system up out of the way, near the ceiling.
Since the speakers are in very close proximity to a large flat drywall surface, the ceiling, I thought it would help if I installed a wood panel directly above and in front of the speakers. I purchased two 3/4" sheets of MDF and glued them together. I'm now ready to cut defractive lines in them with a router but am unsure what types of groves, depth and spacing to cut. If anyone here has advice or specs I would much appreciate it. 

An option is to look up quadratic residue diffuser to make one of them. Your max depth of 1.5" limits diffusion down to only over 2000hz. (The depth is 1/4 of targeted wavelength). You will need dividers between wells since it looks like most of the sound the diffuser "sees" is not perpendicular.

Here is one site: