"9.2.3 EDNS0 incompatibility" is not an EDNS issue at all.

[Jonathan de Boyne Pollard]

CS> $ dig -t soa computer.csharp.members.mac.com.
CS> [...]
CS> The 9.2.3 server then re-issues the query without the OPT RR and
CS> gets an NXDOMAIN with the SOA record in the authority section.

No, it doesn't.  Read the output _carefully_.