Mark,
Your point is well taken, particularly with respect to throughput at the wide belt sander.
Our protocol is perhaps a bit different than other shops because of the product we make. For the most part we build flush inset cabinetry with fully mortised butt hinges. These hinges are the real deal and don't provide any mechanism for adjustment. Everything has to be really straight and really flat.
Our sequences for face frames are as follows:
We rough allocate lumber on a bandsaw then let it cool down for a day or so. It doesn't do us any good to straighten or flatten it at this time because it will just move around as tension is released and/or it acclimates moisture content.
On day 2 we face joint then run the stock through a 2 sided planer. This planer never changes height. Everything that comes off the planer is 24.5mm thick, every time. The material is now flat enough to clamp back to a cabinet box but not yet to final thickness.
On day 3 the stock is face sanded on our Butfering double headed widebelt. At this point the material goes (face down) through a dedicated spiral head planer that is set for 22mm thickness.
The sander itself has a digital read out but is not real reliable for calibration. Thickness depends sometimes on who is running the stock, which side of the belt they use, how old the belt is, pressure, feed speed etc. The 22 mm planer gets us 22 mm every time.
Cross grain dimension is accomplished with a dedicated shaper that is set up with a fence-away system like you would stick a door. This shaper also has shear cutter head that produces a pretty clean edge.
The goal here is to produce face frames that never have to go through the wide belt sander after they are glued & pocketscrewed. They are consistent thickness and sanded on the front face.
This helps to produce consistently square openings (which minimizes fitting work for the door later).
We also have a similarly byzantine system for fabricating doors. I won't go into the scary details of that one yet. Suffice to say any greenhorn can produce an extremely flat door with any lumber the vendor ships. The diminished learning curve and predictable outcome makes this seem worthwhile.
The WIXEY thing is in the process of being set up right now. We're installing it with magnets so there isn't much investment if it turns out we should follow everybody's advice about the ProScale.
Will report back.