how good really

They are THAT good.  I purchased 6 McIntosh components from Audio Classics in the past 12 months.  I am convinced.

+1 stereo5! Those Khorns are enduring classics! And a good match with the Mc240!

There are now beryllium diaphragms available for some horns. They have less breakups and so sound smoother and faster. Crossover capacitors have improved as well. Throat and horn designs have improved due to Computer Aided Design, and so have less 'horn' artifact.

There are better coupling capacitors that are more transparent and smoother sounding- for example V-Cap Teflon.
It is possible to run balanced lines if you have a balanced line preamp. This helps prevent colorations due to interconnect cables, and might allow you to run shorter speaker cables, which can help impact and resolution.

There are simpler tube amplifier circuits that are also wider bandwidth and more transparent, with less IM distortion. So there are better things out there.

The Khorns and Klipsch in general hav3 a lot of potential their Xovef parts 
even at best are average at best. I have been into Loudspeaker ,and electronics c modding for yours . I know Parts  quality Very well.
 For example formoneys spend the Jantzen was foil inductors are a great buy 
vs the Top dog Duelunds ,which too are one of the top capacitors ,as well as    VH Audio -CU capacitors , and Jupiter Copper foil  top 3 in my book .
i just installed several of  the Small , .01 Duelund Silver Foil Bypass capacitors 
at $100 each a lot ,as well as the Vh Cu .022 for resolution a great combination .
there are a lot of cost effective ways to better your speakers .
i made Something very similar to the Zobel  networks that Synergistic Research calls Carbon a Xover enhancers ,they charge $450 ,and inside that tube 
nothing special  a resistor,capacitor in series ,to your Loudspeaker terminals .
go build apair. Resistor values , and your speakers are the only  thing you need to experiment with. I help people all the time tuning , wiring upgrade ,
and they even have fancy hardwood hornsthat improve the sound some are $500 
or so but well worth it for a klassic Khorn. I was at a demonstration Paul Klipsch 
did in the early 80s hooked up his Khorns to a 9v am,fm radio , and filled the room with music ,at 104 dB , take a nice SET Amp like a 300b 7 Watts pure bliss.
i Vacuum Tube Expert builder  Radu Tarta ,I have bought several custom Vacuum Tube amps and preamps  .much less then the big names and far better 
all Top quality parts ,and transformer coupled . Just for the Audiophiles That 
demand top quality and you choose the woods , powder coating ,colors.
just to give you something to ponder. Zebrawood K horns are my favorite .
they  just started making them again .at onetime exotic woods were allways an option.  Being Audiophiles there are allways tons of options .
getting the most out of your equipment .modding will allways get your much more fhen buying new  for most of the moneys goes into the Top qualityhot rodded Parts . I sold audio and owned a store ,and learned tons from the audio technicians. That is how Modwright got started ,and evolved.