I would say, use coaxial digital or toslink/SPDIF connections to get the best digital connection possible on the 568.1
I would advise you to enable High Speed output on the source that you are connecting too, this should improve the sound quality.

I have not used my 568.1 in a long time, but the 568.2mm I am using now has a multichannel digital input.
Perhaps that is the kind if input you where thinking about.. ?

Anyway, I would also advise you to run the latest firmware on your 568.1, as far as I can remember that is 1.55

#1 568.2mm, HD621, G91DH, 513, 511, DSP3100 , DSP33C , DSP33, 2x MJ Pro 50 MKI, M1500
#2 G68J, HD621, DSP3100, DSP5200HC, DSP33, 3x MJ Pro 50 MKII, MS200, SB Touch, Vertex 2
#3 G61rsl, HD621, 596P, DSP7000, DSP5500HC, DSP33, 2x MJ Pro 50 MKII, M1500

Applied mods: NOS-SRx Filter by Mr. Apodizer
Mr. Apodizer Digi box