Hello. I recently (yesterday) faced this frontend for linuxsampler, which is claimed to be jsampler rewriting. Unlike jsampler, however, it doesn't support orchestras, which are not even LS feature, and are thus exclusive for JS. It uses gtk and in one review claimed supporting both gtk3 and 2, but current last version (0.3) seems to be last supporting both, because there is relatively recent (just several commits ago) commit, removing gtk2 support.
Build system is autoconf. Choosing gtk version is done by just specifying GTK_LIBS and GTK_CFLAGS env variables for configure (using pkg-config of course). And one drawback: version 0.3 doesn't build with gcc 4.7, because linker gets flag -Wl, which is now valied only for compiler only. In gcc 4.6 there is no problem. To minimize efforts for self i just built it with own versions of CC, CXX and CPP. Not sure, could it be reason, but version, build with GTK3 did not show gui, though it did not freeze and respond to interruption signal (C^c in terminal). My last configuration command was: ./configure --prefix=/usr CC=gcc-4.6 CXX=g++-4.6 CPP=cpp-4.6 \ GTK_LIBS="`pkg-config --libs gtk+-2.0`" \ GTK_LIBS="`pkg-config --cflags gtk+-2.0`" (this is under ubuntu - gcc executable file names lack "minorest" third version digit). It is already packaged for arch in aur: https://aur.archlinux.org/packages/gsampler
