A lot of thanks for your great advice!
I gave up of qmmp and /usr/local and I ve just succeed to install two versions of htop under the control of debian's package manager. There are two htops visible under synaptic: htop(1.0.1) and htop2 (1.0.3 which comes from sid)
You were right. It required to make changes like (htop -> htop2) in makefile.in and makefile.am in places where names of binaries, icons, and man pages were present.
Next I will try to do the same with qmmp.