2 optical devices, 1 optical input on processor

[Triggaaar]

Both my sky+ V1 and xbox (with MS HD kit) can only output digital audio via optical, and my 561 only has 1 input.



I have two choices:

1) Get an optical switcher (not too much hassle, as I will have to go over to the xbox to switch on anyway

2) Get optical converted to digital coax



Questions:

How much does either option affect quality?

Which optical out is better quality, sky+ or xbox?

If the switcher/converter I choose affects quality, how much is it then worth spending on the cables that go with it?



Thanks