The SPDIF output on the X3 is a great bonus, but it is not really intended to be a stellar performer (compared to a dedicated desktop unit), so the main bottleneck would be the SPDIF output of the X3 itself. 44.1kHz is OK, but 192kHz is getting to a very dodgy speed for SPDIF.
Most modern DACs should lock on to the 192kHz from the X3 fine, but if you are using some ancient or badly designed DAC then you might get some lock issues (let alone quite a messy jitter spectrum). In that case, replacing the 3.5mm adaptor cable provided on the X3 might make some difference. I just made up a custom 3.5mm to BNC SPDIF cable and it certainly made a big difference to the signal quality by eliminating strange reflections.
Edited by sandalaudio - 8/7/13 at 11:08pm