Here is what I think is your Quartet I don't know what the reference to Heresy X is though. Also I can't make out the cap value but I'm guessing 50uf and the Inductor for the tweeter looks like the fairly standard .16mH that the Forte uses.
As Moray say's here
"Bob rebuilds the original network and in most cases he only installs new same value capacitors sometimes he will also install upgraded auto transformers. So in a nutshell Bob's networks are Klipsch networks. Al Klappenburger does modify the circuits. Best regards Moray James."
I haven't seen anything from Al on any work for the Quartet.
To get some of what I have from my modified Forte's from Quartets you would have to at least go North Creek 12AWG on Inductors and that would set you back $334 you can use everything in Bob's networks just substitute the Inductors and you should notice a whole different animal. The North Creeks will be big but you can mount them on the cabinet side walls or possibly the on the bottom of the cabinet. I would use nylon tie mounts with brass screws then nylon tie them down. So your basically just putting additional wire onto the inductors with crimp ends the same size that Bob uses and you disconnect Bobs inductors and connect the North Creeks.
If your thinking about possibly someone else's inductors you'd better think again read this
http://www.audioasylum.com/forums/hug/messages/14/147282.html
Why did the other inductors sound different read this North Creek FAQ's and what the difference is between AWG's
http://www.northcreekmusic.com/COILS.html
And if you went 10AWG it would cost $560 for the four inductors.
The $334 in not to much to ask IMO. These inductors get a grip on the bass that has to be heard to be appreciated. But of course your associated gear has to be capable as well. If the associated gear is not up to par with the speaker then one thinks the mods shed little improvement. One just can't depend on the speaker alone. Its a system as a whole. Really its the weakest link that is actually expressed in the system.
I always like to say if you love them go for it.
Other alternatives, if I had to choose between your Quartet and your RF35's I see you own I think I'd try the RF35's they maybe less costly. Even though I have some reservations about an 8in woofer in a two way as if the past I found they just didn't have the speed to be used. The mid's always sounded lethargic lacking in impact. But then again I have not heard a two-way using North Creek Inductors either with an 8in two-way speaker
I have heard DaveC's RF25's with 6.5in woofers and they are spectacularly musical with very plentiful bass. Although looking at the RF25 spec's one would believe they might not go deep enough. Though listening to DaveC's RF25's you really don't notice any real low end grunt missing. The thing about the North Creeks is they give you body and coherency with control throughout their working range this is why they may work very well with an 8in woofer giving the 8in a chance while common Iron Core's are simply vague with not much control in my experience. Think about the upper range beyond a sub like 120hz to 700hz or so not good with iron core inductors IMO real missing information and impact. BTW the North Creek tweeter Inductor gives a smoothness so much most people tell me they wouldn't even know they were listening to a horn speaker unless they were told.
DaveC did his RF25's for a $600 investment plus the cost of his speakers $600. $1200 total. IMO it would cost 3-$4000 to get what I like from his modified RF25's in a commercial product. they are a joy to listen to and you can listen all day and never tire of them.
So since you have a sub even if you wanted more low end you part with the quartets and pick up the RF25's for their magical mid range. BTW even with the stock crossovers they are one the more musical Klipsch speakers I have heard with factory networks but of course with mods they are a sheer delight and I can tell you more then one person has been wowed by them and they are running on 10 watts of 300B tube power :scratch2:
A lot of fun.
SET12