Differences you can see here in my Excel:
https://forum.rme-audio.de/viewtopic.php?id=35156
UCX II is a USB2, 20ch interface without MADI and only 1x ADAT I/O
MADIface XT II is USB3, 194/196ch interface with 3 MADI buses, but no ADAT I/O, no instrument inputs, lower Mic gain, no DURec.
If you considered getting an XT II (for €2399) but won't need 3x MADI I/O, then you are IMHO better of getting either
one of the two flagship interfaces UFX II (USB2, 30ch, €2099) or UFX III (USB3, 94ch, €2649).
With the flagship interfaces UFX II and III you have the excellent converter of ADI-2 Pro FS series of reference converters and all features that you might need. Autoset, DURec, Mic Gain up to 75 dB, RoomEQ, Crossfeed, Instrument Inputs with higher gain range and separate ports for ARC USB and WC.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14