X-Sabre vs Gungnir
No contest. X-Sabre takes resolution to the next level. Smoother, more open, more detailed, more air, even better bass control and texture. No downside in upgrading from the Gungnir, except the price of course.
X-Sabre vs Concero
Sound is very similar. Detail and air goes to X-Sabre barely. Attack perhaps slightly better. There are several areas where the X-Sabre has a very small advantage, and the Concero at best equals the X-Sabre, so no advantage areas, except price. Largely the decision on these units comes down to features. DSD/DXD + Balanced and slight sound gains vs $500.
X-Sabre vs DA11
Smoother and clearer than the DA11. DA11 is voiced a little different. I would say the DA11 is better than the Gungnir, but I did not compare them directly. I preferred the X-Sabre to the DA11, but not by as much as over the Gungnir.
X-Sabre vs PWD2
Did not care for the PWD2. Treble tended to be harsh and felt much less open. Lacks impact and attack. I think I would even prefer the Gungnir over the PWD2 but again did not compare directly.