Stacked Large Advents v Cornwalls v Klipschorns

I currently have Advents and have always liked the sound. Please only respond if you have actually heard or ownedat least two of the three options I’ve listed. Will either Klipsch model(purchased as a used/older set) be a noticeable upgrade? What will be the benefit (what am I likely to hear) that makes the purchase worth the added cost? Thanks.
I am quite familiar with all three.
1) Klipschorns
2) Cornwalls
3) Distant third - Advents
The Khorns are amazing if you have the correct room for them, but the Cornwalls are a really enjoyable all-arounder, and an easier fit in more rooms if less exciting dynamically. They're still superior dynamically to the average good direct radiator.
In my opinion, the Advents are just too old, and I don't think they are really even in the same league as the other two.  
I have heard all three of them and stacked Advents are hard to beat if the woofers have been serviced correctly. I have owned 4 Advents since 1974 and I went through them a couple years ago and when people hear them they cant believe how good they sound.

Anyone that says negative things about Advents don't know what they are talking about. 

I have owned all three of these speakers and correctly refurbished Advents in a double stacked setup will give the other a run for their money.
I have not heard the Advents, but have owned Cornwalls, Khorns - and La Scalas. 
Generally agree with roxy54. Of the three, for my systems the La Scalas just didn't deliver. The Cornwalls were quite good and were all original. The Khorns were on a different level. However, I should mention they were quite modified; new tweeter, squaker and crossovers. Also, with the help of a friend who was into Klipsch, they were sealed to the walls. Those speakers, driven by Wavac MD300BM mono blocks with Western Electric 300b tubes putting out 10 beautiful watts, sounded fantastic!
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I fell asleep on the Advents, But then I WOKE UP with the Klipsch!!!!
It's just something about that HORNY HORN'S.
Had all 3, in the order you have them listed. The Advents were superb back in the day. However no match for the Cornwalls, and certainly not for the Khorns. As mentioned above, your room is critical for these speakers to sound right. And what you power them with as well. Hint- Wil Vincent from Autospec is selling a Baldwin modified amp here, One of the best sounding amps I heard with the Khorn. 
There is no contest. When I was a teenager in the 70's my older brother was sold on Advents. I challenged him to an A/B test with my Klipschlike Fraisier IV's..They blew his Advents out of the water. He went and bought a pair Heresy's the next day
   I have had experience with three different sets of stacked Advents, they are very good and fun to listen too. All sets had been recapped with new woofer surrounds. They can deliver some wonky impedance issues so be aware of that. 
   On to Cornwall’s, several sets as well, some with Critz woofers and crossovers, a pair with Mundorf Supremes, one pair stock. I like Cornwall’s, in my opinion much more (dynamic), might be the word, and as expected preform beautifully with tubes. 
   Lastly the Khorns, I’ve experienced a couple pair. One pair was highly modified using ALK Eliptrac horns. The other pair was stock aside from B&C tweeters in aluminum wave guilds, they both sounded fantastic.
The pair with the ALK horns and mods resulted in around a 110db efficiency, these were powered by a Truth pre amp and a SET tube amp of about 6-8wpc. I wish I could remember the amp, maybe a Bottlehead, the tubes look like hydrosodium light bulbs. These were absolutely stellar, everything played was just fun to listen to, when music you normally don’t like gets your toes tapping then they are doing it right. 
The main comparison would be efficiency, stacked Advents are exponentially less efficient than the Heritage speakers by comparison, so the question would include a comparison of the equipment down the line as well.