Any suggestions/recommendation for horn sample sounds?
Particularly Stax, Motown, James Brown style.
Compatible with the MoXF flash board?

I’m in the process of converting the DCP “Brass” library to MO XF format
and that library will likely be available next month.

That said, I’m not sure you realize there is no such thing as a “Stax horn sound” or “Tower of Power” horn sound or “James Brown” horn sound.
What you are thinking of is horn arrangements...the parts the horn players
for those artists played.

The best way to produce good section horn parts is to build them up by
playing and recording individual solo parts...listen to the horn players
on those songs, each player has an identifiable part. It isn’t just three
to six players all playing the same notes.

The other piece of the puzzle is in having/using correct sounds - i.e- blasts, falls, swells, growls, etc in ways players use them in addition to the melodic/harmonic content.