Pass labs x260.8 versus xa160.8

Your original posted centered about the question of why there were so many more used listings of one model versus the other.  

The thing to keep in mind is that while one person's individual experience will tell you about their personal experience (which can be informative on its own), it indicates very little one way or the other about the overall pattern of why there are more used models for sale of one model versus the other.  Pass could provide some insight on the issue, but that's unlikely as those type of sales figures are often considered confidential business info by the company, especially by businesses that are privately held.  That was my only point. 

I have noticed that the XA amps (full Class A) have a thicker and softer sound that the "X" amps.  That's not to say that the X amps are thin (they are not thin sounding at all), but the XA does have a very slightly different sound.  XA being more tonally rich, but in a way more colored as well.  Full Class A is harder to do because of demanding power supply requirements.  That's why they usually aren't high power (160 watts is an extremely high amount of Class A power).

Power does not mean sound quality. 
The devil is in the detail.

Heat is probably the biggest issue with these amps. If you have a sealed room, it can get very warm in there. Cost of running Class A, compared to A/AB is is more expensive as well. Bass will be a bit tighter with Pass Labs Class A/AB amps. The number of XA160.8 listings isn’t really that high, many of them are multiples from the same person.
You should check out the number of Sold listings for Luxman M900u if you want to see a high number. A lot of these amps are resold within the first year of purchase - probably one of the biggest buyer remorse purchases I’ve noticed (if they’re selling them that quickly). Weak bass, and bright highs when pushed by any speaker that requires a good amount of power - good midrange though.

The price of the X260.8 is at the higher end of mere mortal pricing.  Mere mortals tend to keep their equipment longer.  The XA160.8 is at the next level pricing, and those who can afford a XA160.8 tend to turn over their equipment more often because they can afford to do so.