Replace Microsoft NLB with BIGIP 2200S

I clirify a bit the my case. Client (10.172.200.100) contact Microsoft NLB (10.172.200.200) with FQND navservernlb.domain.lcl. Behind the VIP there is a couple of server navserver1.domain.lcl and navserver2.domain.lcl. Both navserverX.domain.lcl have to pass credential to a SQL server sqlserver.domain.lcl (on the same network), so we have to create a delegation on Active Directory for FQDN navservernlb.domain.lcl TCPPORT and username/password.

To replace this situation I have tried to configure a new FQDN name navserverF5.domain.lcl that points to the BIGIP virtual server and created a delegation like navservernlb.domain.lcl. I have configured a SNAT Pool and assigned to the Virtual server. When I try to connect to the VirtualServer (is not a web page but a NAV Client) on the SQL server arrives Anonymous authentication, as the credentials has disappeared between client and NavServer.

Here a more clear schema.

Thank you

Mauro