Hi

Thanks to everyone for their help.

I set custom.py to point to the directory I wanted to install to
(/usr/local/csound5 no particular reason, just to keep things neat)

I compiled with

scons generateTags=1 useOSC=1 buildPythonOpcodes=1 Word64=1
buildStkOpcodes=1 install=1 buildVirtual=1 buildInterfaces=1
buildJavaWrapper=1 buildNewParser=1

having downloaded all the necessary *-dev files from Debian AMD64 unstable.

Ran install.py, then I started jack using jackctl, and ran csound with

/usr/local/csound5/bin/csound -B 4096 -+rtaudio=JACK -o
dac:alsa_pcm:playback_ test.csd

It works!

Just a note, Jack complains if -B is set too low, but I could probably
tweak this in jack.  I just got it working, so I'll see how things go
from here.

Never would have got it working without everyone's help, thanks!

Stuart