I emailed Arturia the following last week
The buttons under Pad Controls, Buttons, and Instruments section can't be assigned at all.
MIDI Learn mode can assign buttons with the"Bank" or "Patt." button lit, but the same buttons in "Seq." and "Tune" and "Song" mode can not be assigned. The assignment dialog never shows up.
The "Bank," "Patt," "Seq," and "Tune" buttons can't be assigned, either.
What would work better (as a product suggestion) is for the Bank, Pattern, Seq, and Tune buttons to be selectable, and for the 1-16 buttons to be assigned just once, with their function determined by the currently selected tab, "Bank," "Patt," "Seq," and "Tune."
The "loop on," "erase," and "copy" buttons are assigned by CC instead of note on/off. Note On/Off would be much better for toggling these. Turning a knob as a binary toggle doesn't make much sense.
A nice guy Jerome responded that "Unfortunately some of the buttons are not mappable indeed. However, I put your case in the Spark's feature request list."
I'm interested in buying Spark 2 software during the promotion period to use with my own MIDI controller (a Livid Cntrlr) but only if it seems like mapping of the 16 step buttons and other sequencer control buttons to a non-Arturia controller will be possible. I looked at the Beta page and in the forums and haven't seen these issues addressed so far so I thought I'd post here to ask - is this going to be on the roadmap? If so, when?
The controller hardware you guys built looks very nice but like many other people I already have a bunch of controllers and not a lot of physical space.