I would expect that S16_LE or S24_LE would work ...
Can you run
aplay -L
and the output from
cat /proc/asound/modules
Just checked the specs on your AVR it's 24/192 burr brown converters so while Snakeoil/jriver-player is sending S32_LE (44100/1) the AVR won't recognise that as a valid HDMI stream.
@"agent_kith" comments ?