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

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.

@opm  Nelson Pass has some amplifiers that are 2nd harmonic dominant (many of the First Watt offerings) and some that are 3rd harmonic dominant (the XA25).  He's found that roughly 1/3rd of listeners prefer each, and 1/3 don't differentiate. 

Any amplifier that has a fully balanced design will eliminate all even-ordered harmonics, and thus will be 3rd harmonic dominant.  

@triodlover1499 Nelson Pass and his company are simply among the best in the industry.  It's just crazy how much time they take out of their lives to support the diy community.  Who else out there is "supplementing" their commercial enterprise with free designs released merely because they want others to have good sound?  Maybe just Duke at Audiokenesis...

@hifi59  That´s the first time I've ever seen a Pass amplifier measure at less than specified power.  On multiple other occasions reviewers have explicitly noted that the amps are very conservatively rated.  

See, e.g., this stereophile review of the XA30.5: 

"Fig.4 shows how the THD+noise percentage in the amplifier's output varies with output power into 8, 4, and 2 ohms. While the XA30.5 may give 30Wpc into 8 ohms in class-A (14.8dBW), the distortion at this power level is low, at 0.015%. The amplifier doesn't actually clip (defined as the THD reaching 1%) until a much higher power level: 130Wpc into 8 ohms (21.14dBW). Even higher powers were available into lower impedances before clipping: 195Wpc into 4 ohms with both channels driven (19.9dBW), and 332W into 2 ohms with one channel driven (19.2dBW)."

And another for the XA25:

"The INT-25's output power is specified as 25W into 8 ohms and 50W into 4 ohms, both equivalent to 14dBW, with a "class-A envelope" of 50W peak into 2, 4, or 8 ohm loads. With "clipping" defined as when the THD+noise reaches 1%, I found that the Pass Labs amplifier with both channels driven at 1kHz clipped at 60W into 8 ohms (17.8dBW, fig.4) and 98W into 4 ohms (16.9dBW, fig.5)."

I think the X350.5 was actually broken.  As he notes, obviously the DC offset needs to be re-biased, and given that power behavior, I think it's in need of more substantial service.