If you are using analogue output, and haven't connected the amplifier as an audio pipe to the media director (using either the setup wizard, or the connection wizard in the web admin), then any volume messages will go to the App Server, which alters the sound card volume....
If you do a device template for your TV, and do not put volume down/up commands in the template, most likely the volume commands will still try to go to the TV, but will not work, because there is no equivalent IR for it. The solution here, is to go into the Connection wizard, right click on the audio connector on the TV, and de-select the audio checkbox from the popup box that appears.
Digital outputs do not have any form of volume control and MUST have its sound output device, be it an amplifier, or powered speaker, able to be controleld in some manner, such as IR.
-Thom