Ok, I gave you a taste of the music. Now, check out the opening to Filmation's interpretation of the Hardy Boys, once again uploaded by Skeebwilcox to YouTube:
I cannot identify the studio musicians appearing as the band in the clip. However, we do know the voices behind the characters. The bulk of the male voices were done by Dallas McKennon (Daniel Boone, Archie's Funhouse). Jane Webb, of course, voiced the Hardys' made-for-TV female sidekick, Wanda Kay. Wanda and drummer Pete Jones, the first African American character to appear in a cartoon, didn't appear in the original books. Chet "Chubby" Morton did, however, and, aside from the Hardys' father, Det. Fenton Hardy, was the only supporting character from the novels to make the transition to the cartoon. Byron Kane, who was previously a producer on shows like Peter Gunn, was the only other actor credited.
RCA released 2 albums spun off from the series. I recall seeing one of them at a record convention several years ago, but by then I no longer owned a turntable, so I passed. Neither record has been reissued on CD as yet. Hardy Boys lasted for 2 seasons, but hasn't seen the light of day since a brief syndicated run in the 70's, presumably to cash in on the live-action series (which lasted 3 years).