Download Lex's ProFX from here:
ProFx Version 3.x
I believe the download titled:
ProFx v3.08 for all 3538 kX driver versions!
will work for kX version 3541.
Lex wrote a guide here on how to use the DSP:
Quick kX DSP Guide (by Lex Nahumury)
There have been changes in ProFX since Lex made the above page. Input options that used to be found entirely in the SRC plugin are divided up between the SRC and ADC plugins.
These pages should give you a good basic understanding of the DSP.