Re: Which analogue crossover is the best?
The Peavey transducer engineering group is not likely to offer advice for crossing over to other companies subs, but surely Peavey has advice wrt to a similar Peavey sub, likewise look at the crossover recommendations from JBL for the subs. That transition is not as critical as the upper frequency crossover filters, but hopefully you can find some common ground between the Peavey and JBL advice.
If the service guys are not helpful maybe you're asking the wrong question. One of the more annoying questions is hey, I bought all this other stuff from your direct competitors, but how do I get them all to work together ? I don't expect Yamaha or JBL service to be any more responsive to asking them about how to crossover to the Peavey tops.
On a slightly related topic, I recall once asking the transducers engineers to give me a set of crossover presets for an inexpensive adjustable crossover plugin in a Peavey power amp, and they declined because they didn't trust the accuracy/repeatability of the crude frequency adjustment in the plug-in. I would not expect this to be as much of a limitation with more precise (at least in theory) digital crossovers. So at least they should have optimal advice. Getting an analog crossover to actually deliver that precisely is another story.
In my experience the Peavey service dept was pretty good, but keep in mind their job is dealing with faulty product issues, not mixed brand system integration. I don't even recognize the UL215H model but I've been outside the walls for several years now.
JR