I think that the aux button includes an sysex address to be edited by the slider data parameter.

I can't edit a complete sysex including F0=data=F7 to an external sound module in the auxiliary button.

When I include de F0 byte it seems that the buffer does not accept a non data byte to be edited.

I'm supposing it works only to Roland internal sysex format, i.e. adresss + data.