I finally get to contribute to this thread being the recent recipient of a pair of JH16s. These are of course my opinions. To preface the review, I have NO PROBLEM paying $1,200 for something and admitting I wasted my money. This is my unbiased review.
If I had to use one word to describe these, it'd be POWERFUL! The quad bass drivers really give these things a deep impact. It doesn't increase the overall presence of bass so muddiness shouldn't be of any concern to a prospective buyer (Unless you listen to certain genres. More on that later), but the lower bass frequencies that get a boost create an atmosphere that you can almost feel. The highs are still bright and the mids are still full.
I wouldn't consider these neutral, however. There is a bass bias, but I would only consider this a deterrent if you listened primarily to acoustic or more vocal oriented music. Anything with a full band and drums sounds FANTASTIC. EXPLOSIVE. However, I can see how someone would be a little disappointed when listening to something softer where the warmness could take away from the more delicate sound of a female pianist singing softly into your ears, for example.
But the way I see it, what may be considered shortcomings just give you an excuse to grab another pair from your collection. I have a pair of 6 driver upgraded UM Mages that sound perfectly neutral to me and I'm pleased that I can still find use for them. From what I've read, the JH13 appear to have a similar sound signature to my UMs. If so, any listener would be perfectly suited to own them both and never have to search for another pair of monitors.
P.S.
For the record, I don't like every pair of custom monitors I've tried. I've never had a pair of universal remolds that weren't fit for the garbage and a few months ago I bought a pair of 8 driver InearZ and immediately sold them for half the price paid. They were absolutely horrible. The 4 driver variation of UM's Mage was also a little underwhelming, hence the upgrade. It wasn't bad, but just wasn't the sound signature I had been looking for.