When my dad and I were plumbing my do-it-ourself system, my dad decided it would be very simple to deliver water into the grow beds using a PVC pipe with holes drilled in it. He drilled 4 holes (2 for each tank) using a 1/4 inch drill bit. I later added 2 more (1 for each tank) with a 3/8 inch drill bit to get more water in the beds and faster.
The problem with this approach as I see it...splatter.
Would it be better to put a T in the center of each tank and deliver the water from the 3/4 inch pipe in that manner? I could actually extend some PVC down from the T slightly below the gravel line. It seems like that would reduce the splatter.
I would not extend water delivery pipe below the gravel (roots will grow into it and you might not notice the reduced flow right away.)
I would probably just let the water flow into the bed unrestricted or as Chi said, more holes, larger holes. If the pipe is right down on the gravel and you aim the holes down, that should minimize splatter but you can still check to make sure they are not clogged.