Your general solution Sol1 should also simplify to an expression with signum(xc1-xc2) without the need to restrict the domain to real
sqrt((xc1 - xc2)^2)/(xc1 - xc2);
simplify(%);
(1/2)
/ 2\
\(xc1 - xc2) /
-------------------
xc1 - xc2
signum(xc1 - xc2)
Perhaps the radical is too complex and Maple overlooks this simplifcation or there is no simplification possible in the complex domain (for a reason I can't see at the moment).
Anyway, your substitution is equivalent to the assumption xc1 > xc2. You could use
simplify~(solve({eq1, eq2}, [x, y], explicit), radical) assuming (xc2 < xc1)
to avoid a call to realdomain and the substitution step. It's just a little bit neater.
Edit:
No simplification to an expression with signum possible in the complex domain without assumptions because the expression bellow is in general not zero