So you would not address the issue with the D50s, fine. I am pasting here what Paul wrote in his website. Keep in mind he did not find out a problem with "compatibility with spdif" as you wrote:
After a raft of email exchanges with Topping, Electromod has issued this statement based upon information issued to it via Topping itself,
“As the UK distributor of many brands, we take product issues very seriously. Since Paul alerted us to the Topping DAC issue, we emailed Topping Audio to try and find out more. Unfortunately, Topping has said that that it cannot resolve the issue. Reportedly, the audio problems heard with the D50s DAC are caused by the Cirrus Logic receiver chip. According to Topping, this chip will struggle to work efficiently if faced with an unstable or irregular signals also called Jitter. This audio issue effects all Topping DACS featuring the Cirrus Logic receiver chip which including the D50s, DX7pro, D30Pro and the new batch of the E30 DACs. According to our tests, this audio drop out issue does not affect other inputs, only the coaxial input. If you have purchased a Topping DAC through Electromod and are having any issues, please call/email us to discuss it further.”