New Post: Lists.asmx 401 cross subdomain, farm admin works

Farm admin can succesfuly updatelistitems using spservices, but any other user receives 401.
I tried nearly everything, (disableloopbackcheck) but cannot seem to find the problem. If the ajax call is in the same sitecoll everybody is able to update but as soon as I do a the ajax call from another subdomain (aaa.domain.com updating list in bbbbb.domain.com) it fails for all users , except farm admin.

It must be a config setting (permission) on lists.asmx but I got no clue. Browsing to lists.asmx is ok for all users.

Please help.

Fiddlers says:
HTTP/1.1 401 Unauthorized
Content-Type: text/plain; charset=utf-8
Server: Microsoft-IIS/8.0
SPRequestGuid: 8c697f9c-461a-f0f7-8970-515ac339018b
request-id: 8c697f9c-461a-f0f7-8970-515ac339018b
X-FRAME-OPTIONS: SAMEORIGIN
SPRequestDuration: 5
SPIisLatency: 1
WWW-Authenticate: NTLM
X-Powered-By: ASP.NET
MicrosoftSharePointTeamServices: 15.0.0.4420
X-Content-Type-Options: nosniff
X-MS-InvokeApp: 1; RequireReadOnly
Date: Fri, 21 Mar 2014 11:34:40 GMT
Content-Length: 16
Proxy-Support: Session-Based-Authentication

401 UNAUTHORIZED