Could it be you changed the order of your sound devices prior to sending that command ? It should work. aplay clearly indicated hw:2,0 and hw:2,1 as your sound blaster.
Another possibility is that you do not have alsa-utils installed.
Please force a re-install of alsa-utils .
and then try the following commands (as both a regular user, and also as root) :
speaker-test -c2 -D hw:0,0 -l1 -twav
speaker-test -c2 -D hw:0,1 -l1 -twav
speaker-test -c2 -D hw:1,0 -l1 -twav
speaker-test -c2 -D hw:1,1 -l1 -twav
speaker-test -c2 -D hw:2,0 -l1 -twav
speaker-test -c2 -D hw:2,1 -l1 -twav
where you need alsa-utils installed for the -twav to work .
Another possibility is a permissions issue, but trying with root permissions has likely eliminated that possibility.