DJM900 digital input levels quiet

All, I have recently purchased a pair of coaxial cables to use the digital inputs on my DJM900, however, I now seem to have to crank up the gain (sometimes to the max which I don't like doing) to raise the channel levels to +7db (top of orange, flickering red).  Is this normal?

Could it be that I have used cheapish cables? I thought that digital is digital and it will either work or it wont work at all.

Could it be the source? Currently using Denon HS5500s (soon to move to pioneer!!!), although I cannot find a setting on the decks to raise the output if using digital connections.

Not had chance to do much investigating into this, should do over the weekend, but hoped someone here may know of a reason anyway.

Regards,

Luke