Let us gather here, listen to music what the main characters happy and not so happy times:

Spenser
like: Jazz, Duke Ellington, Sonny Rollins, Johnny Hartman, Benny Goodman (besonders Carnegy Hall von 1938), Dean Martin, Gerry Mulligan / Chet Baker, Lee Wiley, Bobby Hackett,
like not: Hard Rock, Gogi Grant, Country

Hawk
like: Jazz, Soul, Marvin Gaye
like not: Hip Hop

Susan
like: Klassik, Waylon Jennings, Jimmy Rushing, Willie Nelson

Belson: Unknown
Quirk: Unknown

Mean that Hawk Gospel also like ...