McIntosh 452/601 to replace Pass X350.5, good?

I currently have Pass Labs X350.5, speaker is Dynaudio C4 signature.

Generally I love X350.5, doing very good job most of the time. However, it may sound veiled sometimes (usually after 3-4 hours of continuous listening ). Initially I guess it was the heat, because of too much bias, so I start to play with bias adjustment also DC offset etc, and then realized it's so difficult to deal with. Basically it's almost impossible to make bias A and B to be equal, and also the offsets will drift all the time...

I do believe this mismatch bias and drifting DC is the main course of veiled sounding, right?

Anyway, I am thinking McIntosh have an output transformer, which at least will always have 0 DC, should sound clearer? Will it be a good match for the C4 speakers?

I listen to all kinds of music, but classical symphonies is the most concerned.

Thanks for your post.
If the amp's response drifts and sounds veiled at times as you've mentioned, something might be wrong with the amp or other components. Did you have it checked? Great idea to bring in another amp to compare. What are the other devices in the system? Any tubes?
Are you saying you are adjusting the bias on the Pass amp?
Many modern solid state amps are designed to be run with the top lid on. If you're tweaking the amp with the cover off, you are probably defeating any autobias values..
Do not screw around with the offset if you don't work at Pass Labs!

They are the experts!
"Anyway, I am thinking McIntosh have an output transformer, which at least will always have 0 DC, should sound clearer? Will it be a good match for the C4 speakers?"

Thats not a good enough reason to base a purchase on. At the very least, you must demo the McIntosh on your equipment first.

As far as bias goes, something may be wrong with your amp. I never had to adjust bias on any Pass amp that I ever had. Give them a call and see what they say. Of all the MOSFET amp's, Pass is the cleanest.
Unless the 601 has quite a bit more resolution and micro-detail than its predecessor, the 501, I doubt it will sound less veiled than the Pass. I owned the 501 and liked it but always found it a bit veiled in the high frequencies. Great midrange weight, though. You should try to audition before buying.
Get the Pass checked out. If you seek more resolution and detail, the move to Mac would be a step backward in my experience.
not to be flip, but maybe your hearing is drifting...3-4 hours of continuous listening and the human ear/brain system will be changing due to basic body (hormones, etc) dynamics. The pass is the best match for the Dyns. More optimal match across the frequency / impedance band. The Dyns are a complex load. I've heard two different mac's on two different Dyns, and the result was consistent: not as "right" as pass. My ears. My beliefs. Also, AC power into the house changes over time. You'd be surprised how noisy the grid really is.

I think you would be making a mistake in swapping. Unless you are just bored and looking for a change and hunting for problems to justify it--as a former audiophile I have some experience there ;)
I suggest you look elsewhere for your issue.