Pass Labs “House Sound” vs. McIntosh “House Sound”

I´ve not heard the mcintosh but have had the xp20 for some years now and also the same c4s you own. My experience is that most of the time break in is crucial, more so for this preamp.
Out of the box the sound was closed in ,dull and lifeless. So much so, that I felt I had made a mistake in upgrading ? from the pass xp1 after having achieved the performance I was already satisfied with.
But being forewarned by the dealer I reluctantly exercised patience and after what I believe to be several hundred hours ( the dealer advised 500 !) the sound opened up beautifully and have been content ever since. In fact it may be the only piece of equipment that I´ve  never felt the urge to change. At least until now and it has been with me for more than 5 years. 
The xp20 is a fine piece of equipment, dead quiet, with few if any rivals within its price range.

IMO

@rost it’s preowned, so I don’t think I’ll need the 500 hours of break in!  But, I appreciate your comments and am super pumped to get it integrated.  The C2500 was the longest standing piece of my ever revolving/evolving gear setup.  Like a well loved family pet that has since passed, “You are gone, but not forgotten!”

mac house sound?  IME, for example, the MC275 sounds much different from their solid state equipment....

@tzh21y I haven't listened to the MC275's in proper environment.  I don't call listening to them under powering a pair of Sonus Faber's at Best Buy an accurate assessment, which that's the only place I've ever really heard them.