I have build an old version of audacity (audacity-2.4) from source and placed the executable in ~/bin. When I start audacity from the command line (say):
$ audacity-2.4 98.03.14-a.aup
everything runs as it should. But when attempt to start audacity-2.4 from dolphin clicking
dolphin->98.03.14-a.aup->rt-click/Open With->Other Application->audacity-2.4
the program started is audacity not audacity-2.4 . Similarly it's not possible to start audacity-2.4 from the Start Button on the Panel.
I don't have the problem with xv, which I also build from source and placed in ~/bin .
Did you edit the audacity menu item in the KDE Menu (Lower Left) to point to your version? And, if you had a favorite item defined previously for audacity, did you delete that as well?