The piece of script that creates the instrument database in Makefile.am uses $(DESTDIR) as a prefix. When I try to build an rpm from the linuxsampler.spec file the installation step fails because DESTDIR is empty. At linuxsampler.spec.in substitute make prefix=$RPM_BUILD_ROOT%{prefix} install for make DESTDIR=%{buildroot} install and add /var/lib/linuxsampler/instruments.db to the %files section to fix it.
Just commited it to CVS, untested. Hope it works, if not let me know! Thanks!