Gotcha. Yea, no problems what so ever with running a plate with a zex box. Matter of fact, if you were to pop one of them open you'll be surprised to find 2 solenoids and a TPS switch. That's it. As far as adjusting fuel and nitrous based on pressure, that's simply a marketing gimmick. If you were to call and ask how its done they would tell you that as the nitrous flows past the fuel port on the tip of the nozzle as its entering the intake manifold it generates a vacuum on the fuel side. As nitrous pressure increases as does the vacuum and vice versa. Would you be surprised if I told you that just about every nozzle and plate on the market today does the very same thing? Or that the vacuum is so negligible that it hardly makes a difference? And if you were to put it to the test like the original poster did, you'll find that a/f is a mess when bottle pressure isn't within the mfg's preset window and power generation suffers.
Nick