i2s input on X-sabre pro, which streamer

[Lolicon]

First you need a device could output IIS signal.
I'm not sure if the devices you mentioned could do so.
If the sotm sms-200 supports USB output? if so, could try it with X-SPDIF 2? then IIS output to X-SABRE Pro?
I'm not sure if it is feasible, just speculating.

Any chance of a XSP successor soon?

Would love to see a  higher end dac offering than XSP