Something to aware of, depending how well the music is mixed/mastered you could be hearing low mid resonances is the music its self not the cabinet. this is actually quite common in guitar heavy music even in high quality productions from big record labels.
As you say jazz sounds good that makes me lean towards saying its the guitar tracks that have the resonaces as jazz is a typicaly a very warm and fat sounding genre tonally. the same frequencys i suspect you are hearing in the guitar music tracks will be quite prominent in the jazz tracks too just covered by different instruments with different harmonic overtone structures
Id wait until you can get some frequency sweep response measurements to know for sure if its cabinet or the tracks before you start looking into different materials