New sound bar, low volume outputted?

[TheAngryDog]

I've just bought a new sound bar as my previous one was quite quiet.

I've booked this one up and it is the same. I find this surprising. The old sound bar is 40w RMS, the new one is 100w RMS (with a 200w RMS sub).

It is connected via the optical cable from the TV. It sounds the same when connected to my sky box.

When I connect to it via Bluetooth from my phone it is loud.

I have tried it with the sky hdmi cable connected to the hdmi arc port and normal port.

TV is a Sony BRAVIA KD55XE7002
Sound bar is an LG SJ3 300W 2.1Ch Bluetooth Sound Bar with Wireless Sub
Sky box is a 1tb sky+ box.

Any ideas? Thanks.