Squeezeslave seems incompatible with Slimserver 6.5.1. It registers with the server, accepts having a song added to the playlists, but then nothing happens when you start it playing from the webserver:

# /usr/local/bin/squeezeslave 10.0.0.61 -m 02:00:00:00:00:00 -d slimproto -d slimaudio
proto state=1
Output devices:
0: /dev/dsp
slimproto_connect(10.0.0.61, 3483)
proto state=2
Connected to 10.0.0.61
proto state=3
slimproto_send: cmd=HELO len=10
slimproto_recv cmd=vers len=11
slimproto_recv cmd=strm len=30
strm cmd q
slimproto_send: cmd=DSCO len=1
slimaudio_stat strm 0 0
slimproto_stat
        code=strm
        decoder_buffer_size=1048576
        decoder_buffer_fullness=0
        bytes_rx=0
        output_buffer_size=3528000
        output_buffer_fullness=0
        elapsed_seconds=0
slimproto_send: cmd=STAT len=41
DONE strm cmd q
slimproto_recv cmd=grfb len=8
slimproto_recv cmd=grfe len=1290
slimproto_recv cmd=visu len=8
slimproto_recv cmd=setd len=7
slimproto_recv cmd=setd len=7
slimproto_recv cmd=setd len=7
slimproto_recv cmd=setd len=7
slimproto_recv cmd=setd len=7
slimproto_recv cmd=audc len=7
slimproto_recv cmd=knob len=20
slimproto_recv cmd=knob len=20
slimproto_recv cmd=aude len=8
slimproto_recv cmd=audg len=24
slimproto_recv cmd=stat len=6
slimproto_recv cmd=stat len=6

...

No further output, web UI says it is "Playing" but no sound on the output, and the progress bar does not advance.