I've never used Avia, I have DVE. However, did you try setting your speakers to large? This should ensure that any sound sent to the sub is only coming from the LFE channel. If your speakers are set to small, then any bass lower than the assigned frequency is sent to the sub as well. If Avia is outputting bass to the fronts and LFE at the same time, then that could be what's causing the issue.
I'm not sure if your receiver will show if audio is being sent to the LFE channel or not, but check to make sure that is the case as well.
Try setting your speakers to large and do the test again and see if that makes any difference. You can always change it back when you are done. If nothing else, that will get rid of one possible issue. BTW, if you set the speakers to large and you stop getting audio from the sub, then Avia is not using the LFE channel to send the sub audio which is incorrect. (Like I said, I don't have that, I have DVE, so I'm not sure.)
