Small issue with the Domain Name System (DNS) Server Cmdlets
Microsofts DNS Server implementation will not allow you to create a CNAME at the zone apex as per RFC 1034 §3.6.2.
The error you receive (9709, DNS_ERROR_CNAME_COLLISION
) is a bit cryptic, but you won't (and shouldn't) be able to add it anyways.
On the other hand, placing a CNAME RR at the apex effectively introduces a collision with the NS and SOA records for the zone, at which point the error does make some sense