Disappointment with Pass Labs - I'm looking for something else

Hello, I am new to this forum and my mother tongue is not English, so please forgive me if I make mistakes as I use a translator.

I recently bought an XA30.8 and an XP12. I was very happy but as time went by I began to not feel comfortable with the sound.
After doing many tests, I find that the XA30.8 sounds very very sweet but actually too much. I find it to be a loosely defined amp, somewhat muddy and lacks a lot of air and grip. The soundstage is very closed.

The XP-12 is the worst of the two. It is a previous that removes a lot of resolution and information, without transient attacks and sunken mid frequencies. Instead it brings warmth.

Has anyone of you found the same?

If you ask me, I have a Klipsch Cornwall and a dCS BArtok.

Now I want a capable amp, forceful, something warm, decisive, airy and with a great soundstage.

At first I thought of changing my XA30.8 for X250.8, and changing the XP-12 for a second-hand Audio Research Ref5. I am afraid of this change and continue with Pass, since I can go back to the same thing a bit.

On the other hand I have thought of going for a Luxman 900 combo, since it has very good reviews and from what I have read it could be the winning ticket.
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I'm with @unsound.  This conversation is not worthwhile if you're changing speakers.  System synergy is the critical factor.  I've heard gear sound terrible on one system and spectacular on another.  

Once you buy new speakers, start a new thread and ask for recommendations.  Then send that list to the speaker manufacturer and ask if they've got any favorites from the list, or any others you should really audition.  I don't think enough people use their manufacturers' knowledge to maximize their outcomes.
I have Cornwall IVs paired with a PrimaLuna EVO 400 integrated...it’s a match made in heaven if you ask me.
what version of Cornwall's do you have? if its the older ones that's probably your issue they were not great at detail. if its the mk4's I'd suggest a Tube amp like the LTA linier tube audio, Finale Audio /Triode labs. Luxman is another good suggestion I'd stick with their class A amps though. 

 you do not need the power of those big Pass amps X250.8 waist of money regardless of what others here say. the heritage line are quite efficient and do not need a lot of power to come alive.

I've had Heresy 3, Cornwall 3, and now LaScala's all similar and all very good with the right amplifiers. if you have older Cornwall's i recommend you look at upgrading the crossover to bring the crossover point down to 4500hz from the 6khz you will need to upgrade the tweeter as well if you go this way. google Bob Crites for more information on Klipsch upgrades, there's others but he seems to be the most common and reasonable  pricing.  the new ones have this already. 

I've tried some M60 Atmas-phere amps and they are lovely but for high efficiency i found them a little noisy could have been tubes though.

@cal3713  is right on.  I think system building starts with the speaker choice and the room you're putting them in.  That determines so much of the sound signature you are going to live with, for the most part.  And then you need to find a great amp to mate with those speakers.

I owned the Pass XA30.8, too, and I came to precisely the same conclusion that you did.  Too over-warm and a bit vague sounding, just like a blanket was thrown over the music, IME.  It, of course, didn't sing with my primary speakers, TAD CR-1's (not a happy pairing at all, and under-powered), but I also didn't like my very high efficiency Teresonic Ingenium Silvers (the reason I tried the Pass), for the reasons you find.  And I would note that both of these speaker options come from my "up front / bit brighter" camp, which would normally be a better match for a warmer amp.  The Pass just doesn't fill the bill.

I now have a Luxman M900u, and it has the attributes you say you are seeking - - a lot of definition, wondrous soundstaging, while still retaining a smidge of warmth.  And they do have plenty of drive, their Japanese pedigree aside (where did that blanket statement above come from?!).  However, I honestly can't see it with the Klipsch.  But since you're going to throw everything up in the air with a speaker change, I've offered my amp comparison, FYI.