Side question: M260-M269, could you explain the function of these codes? I'm guessing it's an adjustment for how accurate point to point movements are? Or how many lines the controller looks ahead? Similar to the Fanuc G05.1 Q1 R[1-10]?
Brother has 2 algorithms for dealing with accuracy, path interpolation, and point smoothing. Mode A and Mode B.
Mode A is an older technology that intervenes at the servo level, Mode B is a more advanced algorithm that works higher up in the pipeline, at the path interpolation level. That means a Speedio is processing each line of code, developing the raw servo commands, and sending the results to Mode A for it to work it's magic. Mode B is actually taking over the path interpolation level before any servo commands get calculated.
While Mode A is older, it is a superior (i.e. faster for the same level of accuracy) system for prismatic parts machining and adaptive roughing/HSM applications. Most Brothers in the world are drilling, tapping, facing, and side milling a handful of profiles... for them, Mode A is ideal. It's acceleration profiles are very efficient when dealing with prismatic code, so it is faster than Mode B while maintaining higher accuracy on these kinds of parts. Mode A does some path smoothing on complex surfaces, but it is limited to only 20 lines of look ahed for these applications.
Mode B is primarily for complex surfacing applications. It wants to be fed a stream of G1 moves (i.e. no smoothing out code with fitted G2/G3 arcs), with a tight tolerance. Mode B's primary skill is very fast acceleration control and interpolation - in other words, it is going to take that pile of G01 moves that describe a complex surface and turn them into very nice surfaces with the curve originally intended in the CAD file (or close to it). All Speedios ship with Mode B, but you can optionally buy Mode BII which increases the look ahed to 200 lines and allows you to control the level of smoothing applied to complex contour code.
(Note; Look Ahed in a Brother C-00 control is purely for better path interpolation by allowing Mode B to see further into the code. It is NOT a buffer for preventing code starving because these machines simply do not need it - they are processing each block in 1ms. I've worked hard in testing to code starve my Speedio and I've never been able to do it).
Mode A and B in Brother World combine a lot of functions that Fanuc breaks out into separate technologies. Mode A is akin to AI Contour Control for acceleration control. Mode B is like AICC + Nano Smoothing. Mode A is better than anything Fanuc has for prismatics and in production environments, is often responsible for a 5-10% performance gain over Robodrills on those parts. By contrast, I think Robodrill's AICC + Nano Smoothing is a superior system in intense 3D surfacing applications.
In the Speedio, Mode A was called with a series of M26x codes, while Mode B was called with codes in the M28x range... and this situation has been damn confusing to literally everybody. Especially since we all assumed Mode B was newer therefor must be better at everything, so why not use it all the time? We assumed the only reason Mode A was kept around is because a LOT of facilities that run Brother machines cannot make any modification to the G-code - a Speedio absolutely needs to run the same G-code as the older machines in the fleet.
Brother is solving this by introducing a new High Accuracy Quick Setting function; basically a single interface that can use both Mode A and Mode B with a series of "Modes" with logical names (Rough, Finish, Standard, etc) and a new set of M298 Ln codes to call it.
The nice thing about the Quick Setting function is that I've got 10 slots, any one of which can use Mode A or B as I see fit. "Rough" in my machine is set up for high-speed Adaptive Roughing paths with .03" stock allowances. "Semi Finish S" is set up to use Mode B, lose smoothing, and modest acceleration for semi-finishing applications. Finishing for me is still set to Mode A, while Finishing S uses Mode B - and I choose the appropriate one based on the exact kind of geometry I'm machining. I use NX, where we have the "Method" system to set various things about our path, and my post calls the M298 Ln codes based on that method.
Quick Setting also has sort of a simplified mode that is based on absolute accuracy (i.e. you can only deviate 0.0001" from the programmed path, or you can deviate 0.010"). The screen with the blue graphs on it allows an operator to "tune" the modes with a little more/less smoothing or deceleration. I find both of these functions sort of useless.