yeah man.. all of '76 is liquid gold, jaco in his total prime. chicago mike's trio suggestion is fantastic (called TRILOGUE), as it has jaco in a very sparse setting (T-bonist playing multiphonics, bass, drums), at berlin jazztage festival, playing really interesting, "free but direction'd" jazz.. jaco was the last-minute sub on that gig, for upright bass legend dave holland, and he handles it staggeringly well (in fact, from the audience reactions, it's as if a whole "who the heck is THIS amazing new cat?" cult started that night!).. youtube has GREAT footage of that night, god bless it!, search "jaco trilogue"..
also get a 1974 disc called JACO (it's not his brilliant CBS/Columbia debut cd of the same name).. very groove-oriented nyc free-jazz playing on carla bley and annette peacock tunes, sometimes harsh-sounding quartet of paul bley on a rather nasty rhodes, pat metheny, and bob moses on drums... jaco is really tearing it up, his grooves are a catalogue of the stuff he would bust out all over, during the next 2 years.. there are also GEMS among the dozen or so badly-recorded (cassette walkman recorder sitting on a table) "PUNK JAZZ" cds, which were boots that got legitimized after the "producer" struck a deal with jaco's estate. they're rough sonically, and jaco was on the down curve of his time with us, but i was at many of these shows ringside and i can attest (as do the cds) to long chunks of sheer brilliance, amidst all the goofs and onstage shenanigans.. happy hunting!