Links to the packages I used for this build:

libsndfile-1.0.17
liblo-0.24
fftw-3.1.2
libsamplerate-0.1.2
jack-audio-connection-kit-0.103.0
dssi-0.9.1
raptor-1.4.16
liblrdf-0.4.0
XML-Twig-3.32
fluidsynth-1.0.8

ladspa.h
(You only need the "LADSPA Header File", which needs to be renamed "ladspa.h" and copied as shown below)

Graphical Ints for JACK and fluidsynth -- Note: You want the older (stable) Qt3 versions as specified, below:

Qsynth 0.2.6 (stable-Qt3)
Qjackctl 0.2.23(stable-Qt3)

Lilypond notation editor is a whole complicated build in itself. Luckily, there are currently current Slackware packages at: Johannes Shoepfer's site

I install everything to the /usr tree, as is shown in the "configure" lines below.

# I started with Timidity, but ended up working with FluidSynth instead, so
Timidity is not really pertinent. (but this worked)
#cd TiMidity++-2.13.2
#./configure --enable-network --enable-ncurses --enable-spectrogram --enable-vt100 --enable-server --enable-interface=gtk,motif --enable-audio=alsa
#make
#make install

#================================================================
# libsndfile
#================================================================


cd libsndfile-1.0.17
./configure --prefix=/usr
make
make install

#-=-=-=-=-=-=-=-=-=-= Configuration Complete =-=-=-=-=-=-=-=-=-=-
#
# Configuration summary :
#
# Version : ..................... 1.0.17
# Experimental code : ........... no
#
# Tools :
#
# Compiler is GCC : ............. yes
# GCC major version : ........... 4
#
# Installation directories :
#
# Library directory : ........... /usr/lib
# Program directory : ........... /usr/bin
# Pkgconfig directory : ......... /usr/lib/pkgconfig
# HTML docs directory : ......... /usr/share/doc/libsndfile1-dev/html

#================================================================
# liblo
#================================================================


cd liblo-0.24
./configure --prefix=/usr
make
make install

#================================================================
# fftw -
#================================================================

cd fftw-3.1.2
./configure --enable-single --enable-shared --enable-threads --prefix=/usr
make
make install

#================================================================
# libsamplerate
#================================================================


cd libsamplerate-0.1.2
./configure --prefix=/usr
make
make install

#================================================================
# Jack Audio daemon
#================================================================

cd jack-audio-connection-kit-0.103.0

# add "none /tmp/jack tmpfs defaults 0 0" in /etc/fstab

./configure --prefix=/usr --with-default-tmpdir=/tmp/jack
make
make install

#jack-audio-connection-kit 0.103.0 :
#
#| Build with ALSA support............................... : true
#| Build with FreeBob support............................ : false
#| Build with OSS support................................ : true
#| Build with CoreAudio support.......................... : false
#| Build with PortAudio support.......................... : false
#| Compiler optimization flags........................... : -DREENTRANT -O3 -fomit-frame-pointer -ffast-math -funroll-loops -march=i686 -mmmx -msse -mfpmath=sse
#| Compiler full flags................................... : -I$(top_srcdir)/config -I$(top_srcdir) -I$(top_srcdir) -D_REENTRANT -D_POSIX_PTHREAD_SEMANTICS -Wall -g -g -O2
#| Install dir for libjack + backends.................... : ${exec_prefix}/lib/jack
#|
#| Default driver backend................................ : "alsa"
#| Shared memory interface............................... : "System V"
#| Install prefix........................................ : /usr

#================================================================
# ladspa
#================================================================

cp ladspa.h /usr/include/

#================================================================
# dssi
#================================================================

cd dssi-0.9.1
./configure --prefix=/usr
make
make install

#================================================================
# raptor
#================================================================

cd raptor-1.4.16
./configure --prefix=/usr
make
make install

#Raptor build summary:
# RDF parsers available : rdfxml ntriples turtle trig guess rss-tag-soup grddl
# RDF parsers enabled : rdfxml ntriples turtle trig guess rss-tag-soup grddl
# RDF serializers available : rdfxml rdfxml-abbrev turtle ntriples rss-1.0 dot
# RDF serializers enabled : rdfxml rdfxml-abbrev turtle ntriples rss-1.0 dot
# XML parser : libxml(system 2.6.28)
# WWW library : libcurl 7.16.2

#================================================================
# liblrdf
#================================================================

cd liblrdf-0.4.0/
./configure --prefix=/usr
make
make install

#================================================================
# XML::Twig Perl Module
#================================================================

cd XML-Twig-3.32/
perl Makefile.PL
make
make install
#================================================================
# Lilypond: the music notation editor
#================================================================

# install Lilypond Slackware package

cd rosegarden-1.6.1/
cmake .
make
make install

cd fluidsynth-1.0.8/
./configure --prefix=/usr --enable-ladspa
make
make install



# below is a previous (successful) try at the previous version of Rosegarden.
#cd rosegarden-1.5.1
#cmake .
#make
#
#root@jeroboam:/home/whinery/Packages/Soundstation_Build/rosegarden-1.5.1# cmake .
#-- Found Qt3 (version 3.3.8)
#-- Found KDE3 include dir: /usr/include
#-- Found KDE3 library dir: /usr/lib
#-- Found KDE3 dcopidl preprocessor: /usr/bin/dcopidl
#-- Found KDE3 dcopidl2cpp preprocessor: /usr/bin/dcopidl2cpp
#-- Found KDE3 kconfig_compiler preprocessor: /usr/bin/kconfig_compiler
#-- Program pkg-config found (/usr/bin/pkg-config)
#-- checking for module 'lrdf>=0.3'
#-- found lrdf, version 0.4.0
#-- Found LADSPA (/usr/include)
#-- Program msgfmt found (/usr/bin/msgfmt)
#-- Program kde-config found (/usr/bin/kde-config)
#-- Program meinproc found (/usr/bin/meinproc)
#-- Rosegarden 1.5.1 will be built for install into /usr
#-- Configured to compile for release without debug information
#
#Installation Summary
#--------------------
#
#Install Directory : /usr
#Build type : Release
#Use Qt/KDE precompiled headers: FALSE
#
#Xft notation font support : TRUE
#LIRC infrared remote support : FALSE
#
#ALSA MIDI support : TRUE
#JACK audio support : TRUE
#LADSPA plugin support : TRUE
#DSSI synth plugin support : TRUE
#Custom OSC plugin GUI support : TRUE
#Audio timestretching : TRUE
#LRDF plugin metadata support : TRUE
#
#-- Configuring done
#-- Generating done
#-- Build files have been written to: #/home/whinery/Packages/Soundstation_Build/rosegarden-1.5.1