The only way to read a two-citizen-parent requirement into SR511 is if you also read it to mean that natural born citizens must be born on military bases.
Are you saying that natural born citizens must be born on military bases?
Baloney -- read it again.
The fact that the Senate deemed birth in presumed U.S. territory worthy of inclusion in a Resolution, purportedly affirming that John McCain is a natural-born citizen, is indicative of specific need to do so.
That both citizen parents and birth in presumed U.S. territory were deemed worthy of inclusion in their Resolution, with both the jus sanguinis qualifying status and the jus soli qualifying status, is indicative of specific need to do so.
The relevant SR.511 text in question reads:
"Whereas John Sidney McCain, III, was born to American citizens on an American military base in the Panama Canal Zone in 1936"