Please don't tell someone to reduce their pH in their reactor by 1.0 like it is a fact. A change like that to his system is a likely to cause a tank crash. The OP clearly stated he wants to use the method of a steady stream of effluent and adjust the reactor by adjusting the pH. With a steady stream of effluent and 6.5 to 6.6 pH, he will melt that media so fast his alk will be climbing by the minute.
While you may be running 40mL per minute at a reactor pH of 6.5, that doesn't mean he should be. 40 mL per minute isn't what I would consider a steady stream, as most that are running their reactors by pH tend to be running 80-100mL per minute.
Starting out with a calcium reactor, this approach is a bit easier as they only have to adjust one of the variables to adjust their results. starting out at a high pH is definitely good, as you can always buffer with 2-part to raise your numbers if your reactor didn't put enough in that day at the conservative pH. Add your 2-part to get back to steady numbers, and lower your pH a bit and test again the next day until you find the pH that keeps up with your tanks output. It may not be the most efficient use of cO2, but it works.
His question was related to how to get his cO2 delivery setup to handle the 7.4pH he is attempting to use. The answer he is looking for is to drop the pressure at the solenoid down to 3-4psi. This should get him in the range of a bubble every 5-10 seconds and keeping that high of a pH.