The obvious answer would be to go and find a dealer to audition them in person
I'll try to tackle this one.
First, full disclosure.... I've never heard the Heritage Jubilee. I have never heard the new Khorn..... so, we're getting off to a good start, right?
My thoughts.... if space & funds allow, it is a no-brainer.... Heritage Jubilee 100%, all the way.
Why? Simple answer, larger horns. Now, if your Rice Crispies are getting soggy, you can finish now & know the answer. If you don't mind them getting more soggy, then I'll continue a bit.
You have a stock Dodge Challenger, Vette, other..... going up against a new 911. Odds are the new 911 is going to beat the challengers in almost any way but perhaps cost. Now, let's soup up the "challengers".....but to be fair, give Porsche a chance to soup up the 911..... I'd contend again, the 911 is going to whoop some hiney even with them souped up.
The Jubilee is going to simply make the Khorn sound like a toy speaker when auditioned to side by side. This isn't a disrespect of the Khorn.... it IS a 75 year old design. When PWK set out to create the (what became known as) Jubilee.... (he was originally wanting to create the Khorn II but in the end, felt the new design bested the Khorn by such a margin it deserved its own place atop the lineup of speakers)
Anyway, when he created the Khorn, how many years of experience did he have? I don't pretend to know the answer but given it was essentially after WWII, I'd say not many, if any at all. Later in life, technology improves and he wants to revisit his dream.... making the Khorn a 2-way speaker. Now, we have better drivers, better electronics AND he's now got 50 years of design experience behind him. It shows.
The Jubilee is more coherent (sounds like a single driver type thing) than the Khorn but for MY kicks & grins, it absolutely stomps the Khorn with scale of sound. Yeah, they're both big speakers.....huge even. They however, generally fit into a corner so take up very little room space. So I'm not talking physical size. Go get a 1970's transistor radio..... Heck, make it a full on home stereo. Put on your most favorite college marching band. Now, click your heels and transport yourself to the physical band practice where the full ensemble is in front of you. One might argue that the transistor radio has "full sound", they might argue that they can hear EVERYTHING, they might suggest it sounds good.....heck, they might possibly suggest it can play loud (if they've missed their medications). But ALL of that pales in scale to when you hear the band live. Impact is harder, left/right/up/down is bigger, sound is more loud.... just stomps the radio in all respects.
It's not how LOUD the Jubilee might (will) go, it is how BIG it sounds, at loud volumes AND or, normal listening volumes. It is not a Tuba playing in front of you, it's having your head stuffed inside the tuba for that genuine close up listen!
There really is no comparison.
DIsclaimer: No Khorns, transistor radios, Tuba's nor marching bands were hurt during the disclosure of above. Also, I've owned the 'Underground' Jubilee's for about 16 years now and they replaced Khorns so I've got some mileage behind my thoughts. I knew within probably 30 seconds of hearing the (underground) Jubilee's for the first time that I wanted a pair and the Khorns were gone.