Don't they teach you young whippersnappers logic gates in school nowadays?
*coughs and shakes walking cane in your general direction*
Demount your MFSUs and re-place them in serial order (one after another). Unsure if you need to keep a cable in between them; if it doesn't work without, try putting one there, so that the redstone signals don't interfere with each other.
1.) Set the first MFSU (the one your turbines connect to) to output a redstone signal if full.
2.) Set the middle MFSU to output a redstone signal if partially filled.
3.) Connect both MFSUs to a redpower toggle latch. Make sure it receives a redstone signal on the input coming from the middle MFSU at least once so that it toggles into that state.
4.) Connect the toggle latch to your matter fabricator so that the matter fab is currently switched off. May or may not need a NOT gate.
If set up correctly, what happens is as follows:
- Energy flows into your MFSUs. The middle MFSU will have energy coming through it and will therefore output a redstone signal. But if you set it up correctly, your latch will not toggle yet, because you already made sure it was toggled in step 3.
- The third MFSU will fill up first.
- Afterwards, the middle MFSU will start filling up. As soon as it is completely full, its redstone signal will go dark because it is no longer "partially filled".
- Finally, the first MFSU will fill up as well. As soon as it is completely full, its redstone signal will light up. This will toggle the latch, and the matter fabricator will turn on.
- Because the matter fabricator is now running, the first MFSU will no longer be completely full, and its redstone signal goes dark again.
- Eventually, the first MFSU will be completely empty, and the middle MFSU will start draining. However, as soon as that happens, it is once again counted as "partially full" and its redstone signal will light up. This toggles the latch, and the matter fabricator will shut off.
- Now the middle MFSU will fill up again, redstone goes off, first MFSU will start filling until it fills up and the redstone goes on, re-enabling the matter fab... and so on and so forth.
This setup makes sure you always have two full MFSUs worth of buffer storage that never get tapped by the matter fab (the third and middle one), and it also avoids excessive on/off/on/off flicker that will lag your game with redstone block updates.