What amps should I audition?

I would discuss what is needed to get that home audition. Few dealers (really no dealers) will offer a no cost home audition to a stranger. The dealer has a brand new item, used when it is returned. They assume you will return it. What is in it for them? nothing. All it is doing is costing them.
In order to get a home audition I had known my dealer for 33 years,and had spent $40,000 previously there. He offered a Marantz SA-10 for me to audition cold (I did not ask) for five days, no strings.
So the only sort of deal you could go for is like Audio Advisor accepts returns. The one problem there, is they WILL cut you off if you return a big item. Like that $12,000 amp is the only thing you bought, and returned it? Never again. On the other hand, a few companies. Like the current Carver tube offers, offer money back guarantee, I think so does PS Audio?
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Anyway, I ask If you LIKED the Bryston, why do not want something else? The ’grass’ is NOT greener in unknown products. (Particularly MAC gear. MAC gear SUCKS! soundwise.. Jeez.) Just buy a used Bryston 14B3, pair of 7B3’s, or a pair of used 28B3 and stick to your Niagra preamp idea.
I LIKED the sound of my Magnepan 3.6, so KNOWING THAT I went to 20.7s I am happy. I own a 4B-SST² amp. When I actually have some money again, I will go WITH WHAT I LIKE which will be a Bryston pair of 7B3 or a 14B3.. maybe used, maybe new. Sure I can think what about a different amp. Pass? Maybe a tube Carver? but knowing it is a crapshoot.. I will stick to the Bryston. (which sounds great)
I like to try preamps. so there I do play around. Last try was a Conrad Johnson ACT2. (I am disappointed that it was not way way better than my other preamps.. it is good, just not spectacular) I still use my Bryston BP26. The biggest problem for me in tubes is I play music 8 to 10 hours every day. Wearing out tubes too fast. I WOULD go for a Audio Research preamp. Ref 5SE or 6, except for the tube life. I would have to buy new tubes every eight to ten months. Not interested!)
Back to your needs. I would like to know more WHY, if you liked the Bryston/Nagra. are you not going there? The Bryston used is EASY. (as long as you get the dealer receipt for warranty) The Nagra.. Probably have to save up to buy new. or have the money and search the ads for a long time.. Here elsewhere. every day. (the problem is, high demand stuff is sold the same day. Stuff no one whats you can see endlessly day after day. (A nice phono box I was thinking about the same day it posted? IF I would have clicked buy the moment I first saw it. I might have it. Since I waited ten minutes, dawdling . I lost it.)
I have the feeling you are waffling. You want the best, you are worried, can "X" be better than what I heard as great? MY advice from FIFTY FOUR YEARS of buying audio stuff is BUY what you heard and liked. There IS NO magic other pile. yeah you can TRY.. Spending megabucks and being disappointed AGAIN... THAT is the audiophile mantra. Sadly it is very hard to find anyone willing to loan equipment. The money is just not in it, for them, at all. The only real way is buy used, try it, sell it for what you paid. Plenty of folks do that. They are never satisfied. Since the grass really is never greener.. anywhere.

Reno Hi Fi will allow in home trials of Pass equipment for 10 days.

If your decide to return after trial, then you pay the shipping both ways.

They have good deals on demos, with free shipping, and no tax.

d2girls
  Jbl 4367

You've got a speaker that "can" tear your head off with the wrong amp. You want an amp that is extended at both ends, dynamic, detailed and tight. Yet a must is one that is sssssweet!!
And that's going to be the any of the Pass XA's you mentioned, the bigger the better as the standing Class-A will be higher the bigger you go.

Cheers George 

A couple of thoughts:

1.  I have relied on George's insight a number of times and have always been happy that I have.  I put a lot of faith in his experience, particularly the science behind the sound.  He's great at system synergy, which is really important.

2.  Reno Hi-Fi does offer in-home demo's (and it's fully spelled out on their website).  Beyond that, Mark (the owner), is one of the kindest, smartest and most reasonable people I know in the business.  There's a reason Reno is the largest Pass Labs dealer-- I think in the world.

3.  If you decide to skip the Pass recommendation, buy used-- without question.  There are a ton of unrealistic, and a few realistic, sellers right here on Audiogon.  When you find a realistic seller, you need to be ready to go, though.-- right then and there, or what you are looking at will be gone.

4.  I am a big Conrad Johnson, Pass Labs, Eggglestonworks (speakers), fan.  They all make great sounding, reliable and high quality gear.  And, their products are made in the U.S., which I value, as do many others.

Happy searching and listening.

I auditioned 3 of the amp manufacturers you are considering. The current Pass Int, Accuphase 470 and Lux 509X.  All had a unique sound unsurprisingly and I liked them all for different reasons. The Pass for its control over the bottom end, the Luxman for its top end texture. I now own the Accuphase e-470. It was the sweet spot for me. I use it to drive Dyn Contour s5.4 (87db). It has a very musical sound on the slightly warm side.  I am very happy with the e-470.  The e-480 is also about to be released.  Try before you buy. If you can’t get them home, audition with components with similar characteristics to those you intend to pair with in your own environment.  Happy hunting and enjoy the auditioning.