Troubleshooting headphone amp/integrated amp connection

Fellow Audiogoners,

I recently purchased a Heron 5 headphone amplifier. My gear otherwise consists of a Hegel H300 integrated amp; a Simaudio CD 5.3; a refurbished Thorens (MM cartridge); and an EAR 834P phono stage.

Now I can't seem to properly get the Heron 5 connected to the Hegel. When I use the Pre Out RCA connection on the Hegel, I barely get any sound through the headphones. If the Heron 5 is cranked to the max and the Hegel plays at 14 or 15 I'll hear a very faint sound. I'll get more sound if I raise the volume of the the Hegel, but since the Pre Out connection doesn't cancel out the loudspeaker, it kind of defeats the purpose of using headphones (!). I then tried using the Digital Out on the Hegel -- which required using an external DAC since the Heron only has analogue (RCA and balanced) inputs. This lead to decent sound using my CD player, but no sound at all that I could hear using the turntable (I tried Aux 1, 2 and 3 as inputs to the turntable signal coming from the EAR phono stage). The Heron sounds fine also if I connect it directly to the analogue outputs of the Simaudio CD player, but again this implies not using a different source, such as the turntable.

I'm thinking there has to be a way this can work so I can listen to various music sources I use (CD, vinyl, digital files) by connecting the Hegel to the Heron headphone amp. I just can't figure how. Any advice would be much appreciated!

Martin