If you are seeing 25 it means your remote isn't programmed to control the volume on your TV. 25 is the maximum for the PVR and if you turn up the volume on the TV, you'll see how loud it can get.
I agree double-check the TV itself it not set too low.
Want more potency? Consider high wattage external speakers with a subwoofer. Love the surround sound and it's great for my senile ears.