Not an answer but lets me better format my suggestions than commenting.
Get your hands on some .wav files not sure what aplay supports natively but no point in trying to get it to support something like mp3 if it doesn't already.
Try to eliminate as my conflicting processes as possible by typing this at the command prompt.
sudo init 3
...this should drop you to the command-line only you can eliminate even more by entering single user modesudo init 1
but it might eliminate to much not sure.Log in if not already and type
alsamixer
if its not found trysudo apt-get install alsa-utils
first. Alsamixer will allow you to manipulate the volume with your arrow keys in the interface that it launches.Hit ctrl+alt+f1 this should bring you to a fresh command prompt login again.
Execute
aplay /path/to/sound.wav
the file should start playing.Hit ctrl+alt+f7 to get back to the alsamixer if it is a blank prompt flip through them to find which one it is ctrl+alt+f2... etc etc.
Start adjusting the volume to see if there is a delay.
sudo init 5
to get back your GUI