Late to the question, but I am pretty happy with the 2 channel audio performance of my 105D without mods. I'm using it mostly as a dac fed by macmini / audirvana+ / Schitt Wyrd/ AQ Carbon USBs playing redbook and all formats of high rez including native DSD. The rest of my system(i.e. posted as "Silence of the Lamms") is fairly high end, though certainly not as expensive or trendy as many systems here.
After hearing the Oppo compared to many dacs up to $4k, the only one that I wish I could add to the system is the Schitt Audio Yggdrasil at $2300.
My understanding is that the Oppo is not truly balanced and thus the XLR outs shouldn't be offering any improvement vs. the RCA analog outs. Granted, the inputs of your linestage might make a difference. In my rig, which includes fully balanced linestage and balanced monoblock amps with balanced input, there is no difference between Oppo outputs XLR vs. RCA. YMMV. Cheers,
Spencer