Audio Y Splitter TV sound to Hifi quick question

You might find that you need to adjust the volume on both TV and amp first in order to minimise hiss or hum. IE: Very low volume on the TV with very high volume on the amp may give you relatively loud hiss or hum.

Once you've found roughly where the best adjustments are, you can then use either the TV volume control or amp volume control, whichever is most convenient.