Pairing problem with amp/speakers???

Have you hooked up the 1266's directly to the VSX52? If the speakers fade out at the same volume than it is probably in the speakers, if not than it's probably the XPA.

XPA halves the power onto 4ohms and quarters onto 2 ohms.
It has neither powerful transformer nor good filter caps in the power supply and no room for current reserve. You should use for this amp tube-friendly and efficient speakers. Power cut-down is to prevent clipping and save your speakers.

Don't even think of hooking up XPA directly to your speakers. You may jeopardise their condition and safety.
In the best case the clipping protection circuit will block output stage completely.

XPA is cheap and popular and easy to sell and replace with larger poweramp. Good budget options you may find among digital amps that are also made in China and have better 4-ohm drive capabilities.

Thanks. Any advice on the amp (brand and output) that I should replace the XPA with? Any help in the right direction is appreciated. I have about $1500- $2000 to invest in a new amp. Thanks again.

Which XPA amp do you have? The XPA amps shown on Emotiva's website now are rated down to 4 ohms. I don't know why Marakanetz has such a problem with Emotiva gear, but I've found what I've seen to be good bang for the buck stuff.

Are you sure that your amp isn't over heating?

In any case, if you have 1500 to 2000 to throw at an amp, take a look in the agon classifieds. Your budget can buy you a lot of amp.

Wyred4Sound ST500 is in your price range for new.

"Thanks. Any advice on the amp (brand and output) that I should replace the XPA with? Any help in the right direction is appreciated. I have about $1500- $2000 to invest in a new amp. Thanks again."

If you want some good advice, it would be to stop right there. If I'm reading your OP correctly, it looks like you have a real problem. The sound shouldn't just break up and disappear just because you are running your amp a little hard. Something is either not hooked up properly or broken (or both). You need to figure out what the problem is before you buy anything. Check everything. Look all of your components and cables over really well. Plug your sources into different inputs on your preamp. Swap components out with others. Basically, do everything you can do to isolate the problem. Don't do anything until you figure out, for sure, what's wrong.

Anyway, thats my advice.