Hello dgelas, indeed, currently the A/B presets are different and independent, so it is not possible to store two presets at once. The A/B feature is designed to let you compare two different pianos, or two settings of the same piano.

If you want to be able to quickly load a different preset while playing, you could assign a MIDI event to that preset.
For this, open the Preset Manager using the bookshelf icon next to the Save button, click on the drop-down arrow of the preset you're interested in, and select Assign MIDI Event. This will let you navigate between your favourite presets more easily.

Thanks for your reply Alexis. I prefer the A/B to quickly change for a same preset with for example A = equal temperament B = a different temperament. Or A = low keyboard harpsichord B = upper keyboard, or A = clean Rhodes B = same Rhodes with more bark, some drive etc.

This for different (many) presets, so the A/B change (set to the lower key of my master keyboard, also possible with the C letter of the Mac) is simpler than assigning many midi events.
I will continue to manually select the another preset B for each of my preset change

If you want to be able to quickly load a different preset while playing, you could assign a MIDI event to that preset.
For this, open the Preset Manager using the bookshelf icon next to the Save button, click on the drop-down arrow of the preset you're interested in, and select Assign MIDI Event. This will let you navigate between your favourite presets more easily.

it could be a nice feature !