Really Long XLR

Commercially Available Cables:

Look for reputable brands that offer longer XLR cables at a reasonable price. Brands like Mogami, Canare, and Hosa have options for longer cable runs.
Bulk Cable and Connectors for DIY:

If you're comfortable with DIY, you can purchase bulk XLR cable and connectors to make your own cables. Mogami and Canare also sell bulk cable that is well-regarded in the audio community.
Online Audio Forums: Visit audio enthusiast forums like Gearslutz, AVS Forum, or Reddit's r/audiophile to see what other enthusiasts have used for long cable runs. You can often find recommendations from people who have faced similar situations.

Local Audio Shops: Consult with local audio equipment stores or pro audio shops. They may have cost-effective solutions or be able to provide advice on suitable cables for your specific setup.

Used Cables: Consider checking for used cables from reputable brands in your desired length. Many audio enthusiasts upgrade their cables and sell their previous ones, which can be a budget-friendly option.

When choosing or making your cables, be sure to maintain proper cable management and keep them away from potential sources of interference (power cables, electronic equipment) to ensure the best possible audio quality.

I now use extremely long (70ft) XLR interconnects (Blue Jeans Cable) between my preamp and monoblocks. No issues. The choice of preamp is critical. The one I use (VAC Renaissance Mk V - transformer coupled) can run very long interconnects without any issue.

Setups in shows frequently have long interconnect runs, so it is not unusual.

Well, the new 40 foot XLR cables arrived today.  As mentioned earlier,  I bought a pair of Statement XLR from a Canadian company Audio Sensibility. 

https://audiosensibility.com/blog/products-2/interconnects/#!/Statement-SE-XLR-Interconnects/p/22232352/category=2595836

Hooked them and sat down for a listen.  I honestly wasn't expecting to hear any sonic improvement as my existing cables are the higher end (not top) Morrow interconnects and I've always believed the hype about cables, once you hit a decent level, was just that, hype.  The reason for this purchase was the need for longer cables, not dissatisfaction with the Morrows.

Anyway, I put Tom Petty's "Highway Companion" in my player. I know the disc very well and had been listening to it yesterday.  It really makes my system shine.  Right from the get go I found myself leaning forward in my chair thinking WTF? Am I really hearing a difference ?  I can't put it into words, other than to say the difference was obvious and for the better.  Moved on to State of The Tenor vol 1, by Joe Henderson and then Chick Corea Trio from the Trilogy collection.  Next thing you know, three hours have gone by.  Will burn in improve them further?  I guess I'll see in time. For now, I'm more than pleased with the product.

Thanks again to everyone who chimed in.  Cheers.

It depends if your amp and preamp are true balanced.  If they are something like Mogami is fine.  I run Mogami XLR cables in my balanced system between amp and preamp.  I’ve compared this run to using Cardas Clear XLR that I use everywhere else.  There is no difference in sound.  Now doing the exact same thing in another system I have which is not balanced, there is a pretty significant difference.  I believe Atma-Sphere has some white papers out on this subject.