I disagree with you about the SM manual. Tries to do everything and achieves nothing. Very thin on both recreational and technical. A case of ******** baffles brains. I looked to see if there was reference to a really basic travelling SM problem; how to manage two recreational 11l tanks from a dive resort for example...nothing.
Sidemount is an equipment qualification course - so the theory is really all about history, development and primary use options. The PADI Sidemount Diver does a pretty good job in that.
The 'nuts and bolt's of how to use X, Y or Z cylinders...and A, B or C brands of BCD.... that's the
job of the instructor. The manual isn't there to
teach you how to sidemount dive... it's to give you a baseline of information as the foundation from which an instructor develops your actual equipment skills and competencies.
A manual is a supplement to a course... it is
not the course.
This is one reason why a sidemount instructor
actually has to have some expertise and professional knowledge. With many courses, the instructor can simply
regurgitate the manual. Instructors don't need to know much beyond that...they don't need to be subject matter experts.
That approach goes awry with sidemount... the instructor
needs to have a breadth of expertise and knowledge on the application of sidemount techniques using a myriad of cylinders, configurations and BCD designs.
"
How to manage 2x AL80s when resort diving?".... I could give you more than a dozen options. What'd be optimum depends entirely on a plethora of individual circumstances and preferences.
Sidemount diving application isn't an "off-the-shelf" fit... it's bespoke tailored.