I see いっさい + neg. as meaning "not even a little bit". For example, in this snippet:
I translate that as "Not even a little bit does he make any explanation other than the simplest possible explanation of the volcano representing just a volcano."
I have seen いっこうに being used to express a similar connotation of 'not even a little bit'; for example this sentence.
Is there a difference in nuance between the two or can they be used interchangeably?