ASP proper config to allow CORS in a asmx webservice for POST requests - web-services

Question

I´m trying to setup a server capable to handle CORS, but also capable to return the response in json format.
Tried with various config schemes, but no luck.
I need to do my Ajax requests via POST. With my actual config i´m able to do requests via GET, but currently my response always is encapsulated in XML format.
As stated in ResponseFormat.Json returns xml , my requests must be 'application/json' but when I try to do it in this way I'm receiving a preflight message (Response for preflight has invalid HTTP status code 404).
My web.config (allowing CORS via GET) currently is:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<system.web>
<compilation debug="true" targetFramework="4.5.2">
<assemblies>
<add assembly="CrystalDecisions.Web, Version=13.0.2000.0, Culture=neutral, PublicKeyToken=692FBEA5521E1304" />
<add assembly="CrystalDecisions.Shared, Version=13.0.2000.0, Culture=neutral, PublicKeyToken=692FBEA5521E1304" />
<!--<add assembly="log4net, Version=1.2.10.0, Culture=neutral, PublicKeyToken=692FBEA5521E1304"/>-->
<add assembly="CrystalDecisions.ReportSource, Version=13.0.2000.0, Culture=neutral, PublicKeyToken=692FBEA5521E1304" />
<add assembly="CrystalDecisions.ReportAppServer.Controllers, Version=13.0.2000.0, Culture=neutral, PublicKeyToken=692FBEA5521E1304" />
<add assembly="CrystalDecisions.ReportAppServer.DataDefModel, Version=13.0.2000.0, Culture=neutral, PublicKeyToken=692FBEA5521E1304" />
<add assembly="CrystalDecisions.CrystalReports.Engine, Version=13.0.2000.0, Culture=neutral, PublicKeyToken=692FBEA5521E1304" />
<add assembly="CrystalDecisions.ReportAppServer.ClientDoc, Version=13.0.2000.0, Culture=neutral, PublicKeyToken=692fbea5521e1304" />
</assemblies>
</compilation>
<httpRuntime />
<pages controlRenderingCompatibilityVersion="4.0" />
<httpHandlers>
<add verb="GET" path="CrystalImageHandler.aspx" type="CrystalDecisions.Web.CrystalImageHandler, CrystalDecisions.Web, Version=13.0.2000.0, Culture=neutral, PublicKeyToken=692fbea5521e1304" />
</httpHandlers>
<sessionState timeout="30"></sessionState>
<webServices>
<protocols>
<add name="HttpGet" />
<add name="HttpPost" />
</protocols>
</webServices>
</system.web>
<appSettings>
<add key="CrystalImageCleaner-AutoStart" value="true" />
<add key="CrystalImageCleaner-Sleep" value="60000" />
<add key="CrystalImageCleaner-Age" value="120000" />
</appSettings>
<connectionStrings>
<....>
</connectionStrings>
<system.webServer>
<handlers>
<add name="CrystalImageHandler.aspx_GET" verb="GET" path="CrystalImageHandler.aspx" type="CrystalDecisions.Web.CrystalImageHandler, CrystalDecisions.Web, Version=13.0.2000.0, Culture=neutral, PublicKeyToken=692fbea5521e1304" preCondition="integratedMode" />
<remove name="ExtensionlessUrlHandler-Integrated-4.0" /><remove name="OPTIONSVerbHandler" /><remove name="TRACEVerbHandler" /><add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" /></handlers>
<validation validateIntegratedModeConfiguration="false" />
<httpProtocol>
<customHeaders>
<add name="Access-Control-Allow-Origin" value="*" />
<add name="Access-Control-Allow-Headers" value="X-Requested-With, Content-Type" />
<add name="Access-Control-Allow-Methods" value="GET, POST, PUT, DELETE, OPTIONS" />
</customHeaders>
</httpProtocol>
</system.webServer>
</configuration>
I´m using iron-polymer for the Ajax-requests and combined various content-types. Currently i´m getting my data via GET using 'content-type="application/x-www-form-urlencoded; charset=UTF-8" handle-as="document"'.
I´m having difficulties to process the response due such XML encapsulation. Below are two examples of received responses. How to extract the contents ?
1:
<?xml version="1.0" encoding="utf-8"?>
<string xmlns="http://my.domain/">EF7B48E346BC537F98F9696304CECAFE</string>
2:
'<?xml version="1.0" encoding="utf-8"?>
<ArrayOfCiudad xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://my.domain/">
<Ciudad>
<Codigo>32</Codigo>
<Nombre>BOGOTA</Nombre>
<CodigoDepartamento>Z03</CodigoDepartamento>
</Ciudad>
<Ciudad>
<Codigo>133</Codigo>
<Nombre>CALI</Nombre>
<CodigoDepartamento>Z01</CodigoDepartamento>
</Ciudad>
<Ciudad>
<Codigo>53</Codigo>
<Nombre>CARTAGENA</Nombre>
<CodigoDepartamento>Z13</CodigoDepartamento>
</Ciudad>
<Ciudad>
<Codigo>30</Codigo>
<Nombre>MEDELLIN</Nombre>
<CodigoDepartamento>Z04</CodigoDepartamento>
</Ciudad>
</ArrayOfCiudad>'