What would be involved in updating Hersey II’s to Hersey IV’s?

Increasing the size of a previously sealed cabinet is clearly based on the design and tuning of the port relative to the woofer...I’m sure they wouldn’t bother otherwise. Also, Heresy IIIs (and other "heritage" models) simply sound excellent "leaving the factory floor" without ANY mods, and modifying an older model to bring it up to newer model standards isn’t the same thing...obviously...you clearly don’t need to "go big" for horns to sound great, as proved by the Heresy III...you simply need to listen big and stop worrying about porcine makeup. Klipsch manages to make horns that sound like music and provide astonishing levels of efficiency that the "woofers and a tweeter in a box" just can’t do (the efficiency part anyway), and having been able to compare Heresy IIIs to a couple of pairs of excellent albeit more conventional non horn "tower" speakers, over months with my own stuff, the similarities were more profound than the differences...other than efficiency, the fact that all great speakers convey what you give them is undeniable, and well thought out modern horn designs can simply do that more efficiently. My other non horn speakers were sold.

Usually a sealed cabinet requires a larger cabinet. Obviously I dont agree and think that the Heresy and to a slightly lesser degree the Fortes dont sound like real music. I will give you the efficiency part, but all other aspects fall short of others designs in my experience. I have been listening to Klipsch for over 30 years and they just arent my cup of tea. The one thing I have found is that feeding Klipsch with as much tube power as is possible helps the speakers. This comment is more about the behavior of lower powered amps than the speakers. I would be interested in what other speakers you have compared with the Heresy in your home. 

One thing i like about the Heresy is that they are sealed... they have really tight bass and no port noise.   I'm curious to hear what a ported Heresy sounds like , it's heresy to port the Heresy in my opinion.

" Not my cup of tea ". @jsautter ...Same for me, with your overpriced loudspeakers. To me, they sounded compressed, mellow, seamed to be weak, with the leading edge of instruments, and did not, for me, have that " jump " factor, I look for, which my Lascalas give me, in spades......Granted, they played a nice image and soundstage, and offered good coherence from top to bottom, but imo, sounded like a speaker, and not like live music ( interesting, how we differ as to what live music sounds like, or, should sound like ). You can be a negative voice on any Klipsch thread, as you are not the 1st, nor will be the last, but the truth of the matter is, I am happy with the Klipsch Heritage line ( have been for 50 plus years ). The fact that they can be modified and upgraded easily, and affordably, simply creates a better music producer, for me, and others, and, crazy good at the prices, too..........However, unlike you, I will respect you, for liking what you like....So, why bother coming on here, trolling. BTW, my descriptions of your speakers, fits many others, I have owned, sold, and installed for others. Different flavors, for different tastes. Enjoy ! MrD.

@oddiofyl , fyi, there have been Heresy type speaker designs produced by Klipsch, for the live / pro side of their business, and the cabinets were ported, using a different woofer. These model 4s will be the best of the Heresy line, imo.