I would still prefer HDMI over optical, since HDMI will support Multichannel PCM from the Xbox for lossless audio, and as far as I know optical is only limited to legacy DD/DTS and 2 channel PCM.

Running a Xbox One X here just fine over an HD621, it gives me full lossless 5.1 Multi channel PCM, I can even go up to 7.1 if I want to.

I don't go over 5.1 here, so 7.1 or DTS-x/Atmos are not needed for me.

#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