12. Does X5 3rd gen support DoP (DSD over PCM) via Coax out? And what sample rate is supported?

A: Both X5 3rd gen/X7MKII can suport DOP feature via Coax out. And it just can support DSD 64 (2.8MHz/1bit) after setting to DOP. 
How to swtich DOP and D2P: Setting-> Audio settings -> DOP/D2P

Btw, if your X5 3rd gen does not have DOP/D2P option, then please try to upgrade to the latest firmware firstly