Zumbo, -10 to -4 seems a bit excessive but in my experience with the RX-V2400RDS you do need to open the "Tap" just a little more than you do with say an equivalent Sony for example, to listen to DVD movies I have to set the amp to -20, for CD -38 and both the internal tuner and PS2 are happy at around -44. I can't explain why this is so but after a while it won't matter to your dad as I am sure he will be delighted with the sound of his new reciever.